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BOOK    595.7.C73   c.  1 

COMSTOCK    #   ELEMENTS   OF    INSECT 

ANATOMY 


3    T153    OOmsSfiM    1 


THE    ELEMENTS  ^^q 


INSECT  ANATOMY 


AN  OUTLINE  FOR   THE  USE  OF  STUDENTS 
IN  ENTOMOLOGICAL  LABORATORIES 


BY 

JOHN    HENRY   COMSTOCK 

PROFESSOR   OF    ENTOMOLOGY    AND   GENERAL    INVERTEBRATE   ZOOLOGY 
IN   CORNELL    UNIVERSITY 


VERNON    L.    KELLOGG 

PROFESSOR   OF    ENTOMOLOGY    IN    LELAND   STANFORD,  JR.,  UNIVERSITY 


FO  UR  TH  EDI  TIOX,    RE  VISED 


ITHACA,    NEW    YORK 

COMSTOCK    PUBLISHING    CO. 

1902 


Copyright,  1899,  by 
JOHN   HENRY   COMSTOCK 


PREFACE 

The  course  of  study  outlined  in  the  following  pages  is  de- 
signed to  enable  students  to  learn  the  more  general  features 
of  the  structure  of  insects.  It  may  serve  as  an  introduction 
to  a  more  extended  study  of  insect  morphology. 

While  the  more  obvious  object  of  this  course  is  the  learn- 
ing of  certain  facts,  a  much  more  important  thing  to  be 
gained  is  a  training  in  methods  of  careful  observation.  The 
student  is  urged,  therefore,  to  do  the  work  with  great  care. 


CONTENTS 


CHAPTER  PAGE 

^  I.  Terms    Denoting    Position    and    Direction    of 


Parts 


II.  The  External  Anatomy  of  a  Locust,  Melanoplus 

feviur-riibruiii 7 

III.  The   Internal   Anatomy    of  an    Insect,  Corydalis 

cormiia 31 

IV.  The  Anatomy  of  the  Larva  of  the  Giant  Crane- 

fly,  Holorusia  riibiginosa 54 

V.  The  External  Anatomy  of  a  Beetle,  Ptcrostichus 

californicits , 63 

VI.  The  Mouth-parts  OF  Insects 74 

VII.  The  Venation  of  the  Wings  of  Insects 86 

A  VIII.  Methods  of  Insect  Histology 121 

Index  and  Glossary 140 


CHAPTER   I. 
TERMS   DENOTING    POSITION    AND    DIRECTION   OF   PARTS. 

Need  of  a  technical  nomenclature. — It  has  been  found 
that  the  use  of  the  terms  upper,  lower,  inner,  outer,  before, 
behind,  anterior,  posterior,  and  similar  expressions  in  the 
technical  descriptions  of  animals  or  their  parts  frequently 
leads  to  ambiguity.  A  great  part  of  the  confusion  doubtless 
arises  from  the  fact  that  the  natural  position  of  man  differs 
from  that  of  the  lower  animals  in  being  erect.  Thus,  for  ex- 
ample, when  applied  to  men,  before  means  in  the  direction 
indicated  by  a  line  drawn  from  the  center  of  the  body  to  the 
ventral  surface  ;  in  the  lower  animals  it  means  in  the  direc- 
tion indicated  by  a  line  drawn  from  the  center  of  the  body  to 
the  head.  The  same  difificulty  attends  the  use  of  the  term 
anterior  ;  and  of  the  opposite  of  these  terms,  behind  and 
posterior. 

Another  source  of  confusion  in  the  use  of  this  class  of 
terms  is  the  fact  that  they  are  very  commonly  applied  with 
reference  to  the  plane  of  the  horizon.  Thus  above  means 
towards  the  zenith  ;  behic,  towards  the  nadir  ;  and  before  dind 
^M/W  indicate  directions  parallel  to  the  plane  of  the  horizon. 
Consequently  whenever  the  position  of  an  object  is  changed 
the  terms  denoting  the  relation  of  its  parts  must  be  changed. 

In  order  to  avoid  these  difficulties  a  special  set  of  terms 
for  designating  the  position  and  direction  of  the  parts  of 
animals  has  been  adopted  by  many  writers  ;  and  it  is  the 
object  of  this  chapter  to  define  such  of  these  terms  as  are 
used  in  this  book. 


Constrtiction  of  the  terms  used.— Excepting  the  noun 
meson,  the  terms  used  in  this  work  for  denoting  the  position 
and  direction  of  parts  are  either  adjectives  or  adverbs. 

The  adjectives  end  in  <?/,  as  dorsal,  ventral,  and  mesal  ; 
the  adjectives  cephalic  and  intermediate  are  exceptions  to 
this  rule. 

The  adverbs  are  formed  by  substituting  for  the  adjective 
ending  the  ending  ad,  the  Latin  equivalent  of  the  English 
suffix  ward.  Thus  from  the  adjectives  dorsal,  ventral,  and 
mesal,  are  formed  the  adverbs  dorsad,  ventrad,  and  mesad. 

In  forming  compound  words  indicating  position  or  direc- 
tion, the  vowel  o  is  substituted  for  the  termination  of  the  first 
member  of  the  compound,  as  dorso-ventral,  caudo-cephalic. 

The  six  cardinal  directions. — There  are  six  principal 
directions  to  which  the  position  and  direction  of  the  parts  of 
a  bilaterally  symmetrical  animal,  like  an  insect,  are  com- 
monly referred  ;  these  are  as  follows  : 

The  cephalic  direction  or  headward  ;  this  is  the  direction  in- 
dicated by  a  line  drawn  from  the  center  of  the  animal  to  the 
head. 

The  caudal  direction  or  tailward  ;  this  is  the  opposite  of  the 
cephalic  direction. 

Two  lateral  directions,  or  towards  the  right  and  towards  the 
left. 

The  ventral  dirMion  or  bellyward  ;  this  is  the  direction 
indicated  by  a  line  drawn  from  the  center  of  the  body  to  the 
ventral  surface  and  forming  a  right  angle  with  each  of  the 
preceding  directions. 

The  dorsal  direction  or  backward  ;  this  is  the  opposite  of 
the  ventral  direction. 

The  adverbial  forms  of  the  adjectives  cephalic,  caudal, 
lateral,  ventral  and  dorsal  are  cephalad,  caudad,  later  ad,  ventrad, 
and  dorsad.  Thus  a  part  which  extends  in  a  cephalic  direc- 
tion may  be  said  to  extend  cephalad. 


It  should  be  carefully  noted  that  cephalad  does  not  neces- 
sarily mean  towards  the'  head  but  headward ;  that  is,  to- 
wards a  point  which  is  in  a  direction  indicated  by  a  line 
drawn  from  the  center  of  the  animal  to  the  head,  but  at  an 
infinite  distance  in  that  direction.  In  other  words,  these  terms 
must  be  used  in  a  way  analogous  to  that  in  which  we  use 
right  and  left. 

Example. — Take  a  figure  of  a  Dragon-fly  with  its  wings  extended  as 
when  at  rest.  Draw  a  line  from  the  distal  extremity  of  one  of  the  wings 
to  the  head.  Although  this  line  extends  directly  towards  the  head  it  does 
not  extend  cephalad;  but  more  or-  less  nearly  mesad.*  A  line  extending 
cephalad  from  the  distal  extremity  of  a  wing  (or  from  any  other  part)  is 
parallel  to  the  cephalo-caudal  axis  of  the  body. 

Differences  between  the  technical  and  popular  uses 
of  cephalic  and  caudal. — It  has  just  been  shown  that  in 
the  use  of  these  terms  it  is  not  the  head  and  tail  to  which 
the  position  and  direction  of  parts  are  referred,  but  to  two 
of  the  cardinal  directions  which  are  at  right  angles  to 
right  and  left.  Thus  we  can  speak  of  the  caudal  part 
of  the  head  or  of  the  cephalic  portion  of  the  tail.  It  will 
be  seen  that  this  does  not  accord  with  the  popular  uses 
of  these  terms  (as  defined  in  the  dictionaries)  according  to 
which  no  part  of  the  body  is  cephalic  except  the  head  ;  and 
of  the  different  parts  of  the  head  one  is  just  as  much  cephal- 
ic as  another. 

Oblique  lines. — The  position  or  direction  of  a  part 
towards  a  point  between  two  of  the  cardinal  points  can  be 
designated  by  a  compound  term. 

Example. — A  part  which  extends  in  a  direction  between  those  direc- 
tions which  are  indicated  by  dextrad  and  caudad  is  said  to  extend  dextro- 
caudad. 

Meson,  mesal,  and  mesad. — Frequently  the  position 
or  direction  of  a  part  is  referred  to  an  imaginary  plane  di- 

*  Mesad  is  defined  later. 


viding  the  body  into  approximately  equal  right  and  left 
halves.  This  middle  plane  is  called  the  meson  [fiiaov,  mid- 
dle). From  meson  are  derived  the  adjective  mesa/  and  the 
adverb  mesad. 

Ectal,  ectad,  ental,  and  entad. — It  is  often  necessary, 
especially  in  the  study  of  internal  anatomy,  to  compare  parts 
with  relation  to  their  nearness  to  or  remoteness  from  the 
surface  of  the  body.  For  this  purpose  the  terms  ectal  (eicros, 
without)  and  ental  (cvto's,  within)  are  used.  The  adverbial 
forms  of  these  terms  are  ectad  and  entad. 

Example. — The  principal  muscles  of  an  insect  are  attached  to  the  ental 
surface  of  the  body-wall,  or  to  parts  of  the  body-wall  which  project  entad. 
The  hairs  or  spines  on  the  body-wall  project  ectad. 

Aspects  of  the  body. — In  describing  animals  it  is  often 
desirable  to  specify  that  part  of  the  body  which  looks  in  a 
certain  direction.  For  this  purpose  the  term  aspect  is  used 
combined  with  an  adjective  indicating  the  direction  in  which 
the  surface  in  question  looks. 

Examples. — Dorsal  aspect,  ventral  aspect. 

Six  aspects  of  the  body  are  recognized  ;  these  are  dorsal, 
ventral,  cephalic,  caudal  and  the  two  lateral.  The  fact 
that  the  outlines  of  the  body  of  an  animal  are  more  or  less 
curved  does  not  interfere  with  the  practical  application  of 
the  above  terms.* 

Proximal,  distal,  proximad,  and  distad.^In  describ- 
ing appendages  of  the  body  (legs,  wings,  etc.)  the  position  of 
parts  may  be  referred  to  the  two  ends  of  the  appendage  by 
use  of  the  terms  proximal  and  distal.  Proximal  indicates 
nearness  to  the  end  of  the  appendage  which  is  attached  to 
the  body  ;  distal,  to  the  end  which  is  free.     From  these  ad- 

*  Cases  occur  where  it  is  desirable  to  speak  of  an  aspect  which  looks  in  a 
direction  between  two  of  the  cardinal  directions.  Thus  we  speak  ot  the  lines  or 
spots  on  the.  latero-dorsal  aspect  of  a  larva. 


5 

jectives  the  adverbs  proximad  (towards  the   proximal   end) 
and  distad  (towards  the  distal  end)  are  formed. 

Examples. — The  proximal  segment  of  the  leg  of  an  insect  is  the  coxa. 
The  segments  of  the  leg  distad  of  the  tibia  constitute  the  tarsus. 

Aspects  of  appendages. — In  addition  to  the  two  ends 
of  an  appendage  four  aspects  are  recognized.  To  these  the 
same  terms  are  applied  as  to  the  corresponding  aspects  of 
the  body  :  viz.,  dorsal,  ventral,  cephalic,  and  caudal.  It  is 
therefore  necessary  to  have  a  rule  by  which  the  correspond- 
ence between  the  aspects  of  the  body  and  of  appendages  can 
be  determined.  In  other  words,  a  definite  position  must  be 
chosen  as  the  normal  position  of  an  appendage.  Naturalists 
are  quite  well  agreed  as  to  what  is  the  normal  position  of 
the  limbs  of  the  Vertebrates.  The  following  are  what  we 
believe  to  be  the  analogous  positions  for  the  legs  and  wings 
of  insects.* 

{a.)  Wifigs. — Extended  horizontally  at  right  angles  to  the 
body  as  are  the  wings  of  a  dragon-fly  {Libelluld)  when  at 
rest. 

{p.')  Legs. — Extended  horizontally  at  right  angles  to  the 
body  so  that  the  convexity  of  the  articulation  between  the 
two  principal  segments  of  the  leg  (femur  and  tibia)  shall  look 
dorsad  ;  and  so  that  the  surface  of  the  tarsus  ("  foot")  which 
is  usually  applied  to  the  ground  when  walking  shall  look 
ventrad. 

The  dorsal,  ventral,  cephalic,  or  caudal  aspect  of  a  wing  or 
leg  is  that  aspect  which,  when  the  wing  or  leg  is  ia  its  normal 
position,  looks  in  the  same  direction  as  does  the  aspect  of 
the  body  which  bears  the  same  name. 

First,  second,  third,  etc. — When  the  members  of  a 
series  of  parts  forming  a  portion  or  the  whole  of  the  trunk 

*  The  necessity  for  referring  to  the  aspects  of  other  appendages  than  the  legs 
and  wings  will  so  seldom  arise  that  it  does  not  seem  worth  while  to  attempt  to 
determine  the  normal  positions  of  such  appendages. 


are    indicated   by    the   terms,  first,  second,  third,  etc.,  the 
cephalic  member  of  the  series  is  the  first. 

Example. — The^fsf  abdominal  segment  is  the  one  nearest  the  head. 

When  the  series  forms  a  part  or  the  whole  of  an  append- 
age of  the  body,  the  first  member  of  that  series  is  the  proxi- 
mal one. 

Example. — The  Jirst  segment  of  a  leg  is  the  one  which  is  articulated  to 
the  body. 

The  direction  of  an  appendage  does  not  modify  the  above 
rule. 

Example. — The  ^rsf  segment  of  an  antenna  is  the  one  which  is  articu- 
lated with  the  head ;  notwithstanding  that  when  the  antennae  are  directed 
cephalad,  as  is  usually  the  case,  this  segment  is  the  one  nearest  the  caudal 
end  of  the  body. 

Intermediate. — In  order  to  avoid  ambiguity  the  word 
mesal  and  its  derivatives  are  used  only  with  reference  to  the 
meso/i.  The  second  member  of  a  series  of  three  similar  parts 
is  designated  as  the  intej-mediate  one. 

Limitations  to  accuracy.— As  the  body  of  an  animal 
presents  but  few  plane  surfaces  or  straight  lines  it  is  often 
impossible  to  describe  the  position  or  direction  of  a  part  with 
absolute  accuracy.  Practically,  however,  one  will  m.eet  with 
but  few  serious  difficulties.  Thus  in  describing  the  direction 
of  a  curved  or  undulating  line  on  the  surface  of  the  body  it 
will  rarely  be  necessary  to  do  more  than  to  give  the  general 
direction  of  that  line  ;  the  reader  will  understand  that  it  fol- 
lows the  sinuosities  of  the  surface  of  the  body. 


CHAPTER   II. 

THE   EXTERNAL   ANATOMY   OF   A   LOCUST. 
{Melanoplus  femur-rubrum.) 

Locusts  or  short-horned  grasshoppers  are  excellent 
subjects  to  use  in  beginning  the  study  of  the  external  anat- 
omy of  insects.  They  are  very  common  and  are  compara- 
tively large  ;  and  the  parts  of  the  external  skeleton  in  these 
insects  are  mostly  remarkably  distinct. 

The  species  which  has  been  selected  as  the  basis  of  this 
outline  is  the  red-legged  locust,  Melanoplus  femur-rubrum, 
which  is  found  in  nearly  all  parts  of  the  United  States. 
Specimens  of  this  insect,  preserved  in  alcohol,  will  be  fur- 
nished the  student,  who  will  be  expected  to  verify  carefully 
or  to  correct  each  statement  made  in  the  text. 

In  order  to  illustrate  certain  points  not  well  shown  in  the 
locust,  comparative  studies  will  be  made  of  parts  of  a  cock- 
roach. 

DIVISION    OF    THE    BODY    INTO    REGIONS. 

The  body  of  a  locust  is  composed  of  a  series  of  more  or 
less  ring-like  segments.  In  the  caudal  part  of  the  body  the 
ring-like  nature  of  the  segments  is  obvious  ;  in  the  cephalic 
part  it  is  less  so.  These  segments  are  grouped  into  three 
regions  :  head,  thorax,  and  abdomen. 

Head. — The  head  is  the  first  or  cephalic  of  the  three 
regions  of  the  body.  Apparently  it  consists  of  a  single  seg- 
ment. 


8 

Thorax. — The  thorax  is  the  second  or  intermediate  region 
of  the  body.  It  is  readily  distinguished  by  its  appendages  ; 
which  are  three  pairs  of  legs  and  two  pairs  of  wings.  It 
consists  of  three  segments  ;  but  as  each  segment  is  com- 
posed of  several  distinct  pieces,  it  requires  considerable 
study  to  trace  the  outlines  of  each  segment.  We  will  return 
to  this  subject  later. 

Abdomen. — The  abdomen  is  the  third  or  caudal  region 
of  the  body.  The  segments  of  which  it  is  composed  are 
more  simple,  distinct,  and  ring-like  than  those  of  the  other 
regions. 

STRUCTURE    OF    THE    BODY-WALL. 

Chitin. — In  studying  the  anatomy  of  insects  it  is  found 
that  in  the  adult  stage  the  greater  portion  of  the  body-wall, 
that  part  of  the  insect  which  corresponds  in  position  to  the 
skin  of  higher  animals,  is  hard. 

This  hardness  is  due  to  the  deposition  of  a  horny  sub- 
stance, called  chitin,  in  the  membrane  which  constitutes  the 
body-wall. 

Sclerites. — The  chitin  is  not  evenly  distributed  through- 
out this  membrane.  Pull  the  head  of  a  locust  so  as  to  sepa- 
rate it  from  the  thorax  as  far  as  possible  without  breaking 
the  skin.  Note  that  the  head  is  joined  to  the  thorax  by  a 
soft  flexible  membrane,  in  which  but  little,  if  any,  chitin 
has  been  deposited. 

Examine  the  sides  of  the  thorax  with  a  lens  and  observe 
that  the  body-wall  appears  to  be  made  up  of  many  distinct 
pieces.  The  integument  is,  however,  really  continuous  ;  and 
in  each  case  what  appears  as  a  distinct  piece  is  simply  a  por- 
tion of  the  body-wall  in  which  considerable  chitin  has  been  de- 
posited.   Such  a  portion  of  the  body-wall  is  called  a  sclerite.* 

*  The  sclerites  are  analogous  to  the  centers  of  ossification  in  the  bones  of  the 
higher  animals. 


Sutures. — The  sclerites  constitute  the  greater  part  of  the 
body-wall,  the  soft  membranous  portions  separating  them 
being  in  rriost  cases  narrow.  Usually  these  narrow  portions 
are  mere  lines ;  they  are  then  called  sutures. 

PYequently  the  sutures  become  entirely  effaced.  We  are 
therefore  often  unable  to  distinguish  certain  sclerites  in  one 
species  of  insect  which  are  distinct  in  another. 

In  such  cases  the  effaced  suture  is  said  to  be  obsolete. 

PARTS    OF    THE    HEAD. 

The  principal  portion  of  the  chitinized  parts  of  the  head 
are  firmly  joined  together  so  as  to  constitute  a  box  which 
contains  what  may  be  called  by  analogy  the  brain  of  the  in- 
sect and  certain  other  important  organs.  To  this  are  articu- 
lated a  number  of  movable  appendages.  The  parts  of  the 
head  may  be  classed,  therefore,  under  two  divisions  :  first, 
the  fixed  parts,  or  the  skull ;  second,  the  appendages. 

THE  FIXED  PARTS  OF  THE  HEAD. 

Compound  eyes. — The  most  striking  in  appearance  of 
tne  fixed  parts  of  the  head  are  the  eyes.  These  are  two  large, 
nearly  hemispherical  bodies  ;  one  on  each  side,  forming  a 
considerable  portion  of  the  latero-dorsal  part  of  the  head. 

Study  one  of  the  eyes  with  a  compound  microscope,  using 
a  low  power.  Note  the  honey-comb-like  structure  of  the  eye. 
If  you  have  difficulty  in  seeing  this,  remove  a  part  of  one  eye 
with  fine-pointed  scissors  and  mount  it  on  a  glass  slip.  Each 
of  the  hexagonal  divisions  of  the  eye  is  a  cornea  of  a  distinct 
eye.  These  large  eyes  are  therefore  compound,  and  each  of 
the  small  eyes  of  which  they  are  composed  is  termed  an 
ommatidium  (plural  ominatidia).* 

'  Formerly  the  ommatidia  were  termed  ocf//i  (singular  ocellus)  ;  but  later 
writers  use  the  term  ocelli  only  to  designate  the  simple  eyes. 


10 

Make  a  drawing  showing  the  honey-comb-like  structure  of 
the  cornea  of  a  compound  eye. 

Note. — The  drawings  illustrating  this  course  should  be  made  with  great 
care,  on  good  paper.  Outline  drawings  are  better  than  those  that  are  shaded, 
as  shading  tends  to  obscure  lines  indicating  sutures.  The  drawings  should 
be  made  first  with  a  pencil,  then,  after  they  have  been  criticized,  the  lines 
should  be  inked. 

Simple  eyes. — Cephalad  of  the  dorsal  half  of  each  com- 
pound eye  there  is  a  small  transparent  hemispherical  body. 
These  are  the  simple  eyes.  There  is  a  third  simple  eye  situ- 
ated in  a  depression  near  the  center  of  the  cephalic  aspect  of 
the  head.     The  simple  eyes  are  termed  ^r^'/// (singular  ocellus). 

Epicranium. — The  larger  part  of  the  skull  appears  to 
consist  of  a  single  sclerite  which  surrounds  the  compound 
eyes,  and  in  the  locust,  bears  the  simple  eyes.  This  part  is 
termed  the  epicranium.  The  cephalic  and  lateral  parts  of  the 
epicranium  are  separated  on  each  side  by  a  suture  which  ex- 
tends ventrad  from  the  eye.  The  ventral  ends  of  these 
sutures  are  joined  by  a  very  prominent  suture  which  forms 
the  ventral  boundary  of  the  cephalic  portion  of  the  epicra- 
nium. 

The  epicranium  is  a  compound  sclerite,  and  differs  in  its 
extent  in  different  insects. 

Remove  the  head  from  the  thorax  and  mount  it  on  a  slen- 
der pin,  inserting  the  pin  in  the  center  of  the  cephalic  aspect 
of  the  head.     The  pin  will  now  serve  as  a  handle. 

Note  the  slightly  elevated  narrow  ridge  which  separates 
the  lateral  from  the  caudal  aspect  of  the  head.  This  ridge 
marks  the  position  of  the  suture  which  constitutes  the  caudal 
border  of  the  epicranium.  Upon  the  dorsal  aspect  of  the 
head  this  suture  is  obsolete. 

Upon  each  side  joining  the  ventral  end  of  the  suture  just 
described  and  the  ventral  end  of  the  one  which  extends  ven- 
trad from  the  compound  eye  is  a  well-marked  suture,  which 


II 

forms  the  ventral  border  of  the  lateral  part  of  the  epicra- 
nium. 

(a.)  Vertex. — The  dorsal  part  of  the  epicranium  is  called  the 
vertex. 

(/>.)  Front. — That  part  of  the  epicranium  which  is  upon  the 
cephalic  aspect  of  the  head  is  termed  X.\\^  front.  In  many  in- 
sects the  front  is  a  distinct  sclerite. 

(c.)  Genoi.— The  lateral  parts  of  the  epicranium  are  known 
as  the  gence  or  cheeks. 

Clypeus. — Examine  again  the  ventral  border  of  that  part 
of  the  epicranium  which  is  upon  the  cephalic  aspect  of  the 
head.  Note  that  the  prominent  suture  bounding  this  part 
separates  it  from  a  very  broad,  but  short  sclerite.  This  is 
the  clypeus. 

Labrum. — Articulated  to  the  ventral  border  of  the  cly- 
peus is  a  broad,  freely  movable  flap.  This  is  the  upper  lip 
or  labrtun. 

Although  the  labrum  is  freely  movable,  it  is  a  part  of  one  of  the  segments 
that  enter  into  the  make-up  of  the  head-box,  and  not  an  appendage,  like  the 
jaws.  The  true  appendages  of  the  head  hold  the  same  relation  to  this  region 
that  the  legs  do  to  the  thorax. 

Make  a  drawing  of  the  cephalic  aspect  of  the  head  ;  and 
name  the  fixed  parts. 

Occiput. — Examine  a  locust's  head  which  has  been 
boiled  in  caustic  potash,  cleaned,  and  mounted  with  the 
caudal  aspect  uppermost.  In  such  a  preparation  the  soft 
parts  have  been  removed,  and  the  walls  of  the  head  bleached, 
so  that  the  sutures  can  be  more  easily  traced  ;  a  specimen 
of  this  kind  will  be  furnished  the  student. 

Observe  the  large  opening  which  connects  the  cavity  of 
the  head  with  that  of  the  thorax.  The  dorsal  half  of  this 
opening  is  bounded  by  the  octiput.  Each  lateral  half  of  the 
occiput  is  triangular,  with  its  outline  well  marked  ;  but  on 
the  dorsal  aspect  of  the  head  the  suture  between  the  occiput 


12 

and  the  epicranium  is  obsolete.  Hence  on  this  aspect  there 
is  no  indication  of  the  line  where  the  occiput  ends  and  the 
epicranium  begins. 

V  Postgenae. — On  each  side  ventrad  of  the  occiput  and 
caudad  of  the  gena  is  a  large  sclerite.  These  form  the  chief 
portion  of  the  caudal  aspect  of  the .  fixed  parts  of  the  head 
and  may  be  termed  \.\^^  postgence. 

The  postgenae  are  separated  from  the  epicranium  by  the 
.narrow  ridge  which  separates  the  lateral  from  the  caudal 
aspect  of  the  head  ;  a  continuation  of  this  ridge  marks  the 
position  of  the  suture  which  separates  the  occiput  from  the 
epicranium  on  each  side  of  the  head. 

In  many  insects  the  postgenae  and  the  occiput  are  not  separate.  As  this 
is  the  case  in  the  more  generalized  insects  the  occiput  may  be  regarded  as  a 
detached  portion  of  the  postgenae. 

Tentorium. — Observe  the  remains  of  the  membrane 
which  connected  the  head  with  the  thorax.  It  will  be  seen 
that  the  postgenae  are  connected  by  a  strong  part  extending 
from  side  to  side,  within  the  head.  This  is  a  part  of  the  in- 
ternal skeleton  of  the  head  or  tentorium. 

Make  a  drawing  of  the  caudal  aspect  of  the  head,  and  name 
the  parts. 

Review. — The  skull  of  a  locust  consists  of  six  sclerites  ; 
three  of  these,  the  occiput  and  the  two  postgence,  pertain  to  the 
caudal  aspect,  one,  the  epicrajiiutn,  constitutes  the  greater 
part  of  the  dorsal,  lateral,  and  cephalic  aspects,  and  two,  the 
clypeus  and  the  labrum,  form  the  ventral  portion  of  the  cephal- 
ic aspect.  The  epicranium  consists  of  the  vertex,  iht  front 
and  the  gence. 

Cervical  sclerites. — In  the  membrane  connecting  the 
prothorax  with  the  head  there  is  on  each  side  a  pair  of  scle- 
rites forming  a  thickened  line  from  the  thorax  to  the  head  ; 
\.\\(tst  ■2iXt.X.\\t  lateral  cervical  sclerites.  In  some  insects  there 
are  also   ventral   and   dorsal   cervical  sclerites.     The  lateral 


13 

cervical  sclerites   are  termed  by   some   writers  the  jugular 
sclerites. 

The  cervical  sclerites  are  probably  remnants  of  a  segment  the  appendages 
of  which  are  modified  to  form  the  lower  lip  or  labium. 

THE  MOVABLE  PARTS  OF  THE  HEAD. 

Under  this  category  are  classed  a  pair  of  jointed  append- 
ages termed  the  antenncz  and  the  organs  known  collectively 
as  the  mouth-parts. 

Antennae. — Just  cephalad  of  each  compound  eye  there  is 
attached  to  the  head  a  long,  thread-like,  many-jointed  ap- 
pendage. These  are  the  antennce.  Each  antenna  is  situated 
in  rt  depression  which  is  known  as  the  antennary  fossa. 

Mouth-parts. 

Labrum. — Although  the  labrum  is  a  part  of  the  skull  it  is 
commonly  regarded  as  one  of  the  mouth-parts. 

Mandibles. — Carefully  remove  the  labrum.  By  doing 
this  there  is  exposed  a  pair  of  jaws  which  open  by  a  meso- 
lateral  motion  of  each  jaw.  These  are  the  mandibles.  Each 
mandible  consists  of  a  single  short  and  thick  piece,  the  distal 
extremity  of  which  is  notched  so  as  to  form  a  series  of  teeth. 

Trochantin  of  the  mandible. — At  the  base  of  the  man- 
dible, between  it  and  the  gena,  there  is  a  small  sclerite  ;  this 
is  the  trochantin  of  the  mandible. 

Remove  the  mandibles.  This  may  be  done  by  separating 
them  with  a  pin  and  turning  each  one  laterad  until  it  breaks 
from  the  head. 

Maxillae. — By  the  removal  of  the  mandibles  there  is  ex- 
posed a  second  pair  of  jaws  which,  like  the  mandibles,  open 
by  a  meso-lateral  motion.  These  are  the  niaxillce.  Unlike 
the  mandibles  the  maxillae  are  very  complicated  organs.  We 
will  return  to  them  later. 


14 

Labium. — Remove  the  head  of  a  locust  and  pin  it  with 
the  caudal  aspect  uppermost  to  a  piece  of  cork. 

Note  the  freely  movable  flap  which  is  the  caudal  part  of 
the  mouth-parts.  This  and  the  crescent-shaped  piece  to 
which  it  is  attached  form  the  lower  lip  or  labiutn. 

The  labium  consists  of  the  following  parts  : — 

Subtnentuvi. — The  submentum  is  the  proximal  part  of  the 
labium.  It  is  nearly  crescent-shaped,  with  long  tapering 
points,  and  is  joined  to  the  membrane  which  connects  the 
head  with  the  thorax. 

Moitinn. — This  is  the  central  portion  of  the  labium;  and 
is  the  principal  part  of  that  organ.  It  is  articulated  to  the 
distal  margin  of  the  submentum.  To  the  distal  margin  of 
the  mentum  are  joined  two  movable  flaps  ;  and  to  each  lat- 
eral margin  is  joined  a  process  consisting  of  three  segments. 

Labial  Palpi. — These  are  the  three-jointed  processes  of 
which  one  is  joined  to  each  lateral  margin  of  the  mentum. 

Palpiger. — The  labial  palpi  are  not  joined  directly  to  the 
mentum.  There  is  on  each  side  of  the  mentum  a  sclerite 
which  bears  the  palpus  of  that  side  and  which  is  called  the 
palpiger.  The  suture  between  the  palpiger  of  each  side  and 
the  mentum  is  almost  obsolete.  Its  position  is  indicated  by 
a  slight  groove  which  causes  the  palpiger  to  appear  some- 
what like  a  segment  of  the  palpus. 

Ligula. — This  is  the  distal  portion  of  the  labium.  It  con- 
sists of  two  large  movable  flaps. 

Hypopharynx. — If  the  specimen  has  become  dry  so  as  to 
be  brittle,  it  should  be  softened  with  a  little  water. 

With  the  specimen  pinned  as  in  last  section,  carefully  lift 
the  ligula  so  as  to  expose  the  maxillae.  Note  the  tongue-like 
organ  which  arises  from  the  labium  and  from  between  the 
maxillae.     This  is  the  hypopharynx. 

Remove  the  labium  and  place  it  on  a  glass  slip  in  a  drop 
of  Canada  balsam  or  glycerine  and  cover  it  with  a  cover 


15 

glass.  Examine  it  with  a  microscope  using  a  low  power  and 
reflected,  not  transmitted,  light  {i.e.,  turn  the  mirror  so  that 
the  field  of  the  microscope  is  dark  ;  and  place  the  micro- 
scope so  that  a  strong  light  falls  upon  the  specimen).  Make 
a  drawing  of  the  caudal  aspect  of  the  labium,  and  letter  the 
parts. 

Study  the  distal  end  of  the  distal  segment  of  a  labial  pal- 
pus with  a  higher  objective.  Observe  the  sense  papillae  with 
which  it  is  furnished.     Make  a  drawing  of  this  part. 

Parts  of  the  maxillae. — After  the  removal  of  the  labium 
it  is  easy  to  distinguish  the  maxillae,  of  which  there  is  one  on 
each  side  between  the  labium  and  the  mandibles. 

Remove  a  maxilla  and  mount  it  in  Canada  balsam  or 
glycerine,  with  the  caudal  aspect  uppermost.  Examine  w'ith 
a  microscope  using  a  low  objective,  and  reflected  light. 

Make  a  drawing  of  a  maxilla,  and  name  the  parts,  which 
are  as  follows  : — 

Cardo. — The  cardo  or  hinge  is  the  proximal  part  of  the 
maxilla.  It  consists  of  two  sclerites  ;  the  first  is  the  larger 
and  is  triangular  in  outline. 

Stipes. — The  stipes  or  footstalk  is  the  large,  quadrangular 
sclerite  which  forms  the  central  part  of  the  maxilla. 

Lacinia. — Articulated  to  the  distal  end  of  the  stipes  is  a 
large  sclerite,  which  tapers  distad,  is  curved,  and  is  termi- 
nated by  strong  teeth  ;  this  is  known  as  the  lacinia  j  it  is 
called  also  the  inner  lobe. 

Galea. — Joined  to  the  side  of  the  stipes  near  its  distal  end 
and  projecting  laterad  of  the  lacinia  is  a  part  consisting  of 
two  segments.  This  is  the  galea.  The  distal  segment  of  the 
galea  is  large,  spoon-shaped,  and  covers  the  inner  lobe  like  a 
hood  ;  the  proximal  segment  is  constricted  in  the  middle  so 
as  to  resemble  slightly  a  dumb-bell  in  outline.  The  galea  is 
also  known  as  the  outer  lobe,  upper  lobe,  or  superior  lobe. 

Palpifer. — Joined  to  the  lateral  border  of  the  stipes  and 


i6 

between  the  cardo  and  the  proximal  segment  of  the  galea  is 
a  narrow  sclerite  ;  this  is  Xho. palpifer. 

Maxillary  Palpus. — Articulated  to  the  distal  end  of  the 
palpifer  is  a  long,  slender  organ  consisting  of  five  segments  ; 
this  is  the  inaxillary palpus. 

After  completing  the  drawing  of  the  maxilla  as  a  whole, 
study  the  distal  end  of  the  distal  segment  of  the  maxillary 
palpus  with  a  higher  objective,  and  observe  the  sense 
papillae. 

Review. — The  mouth-parts  consist  of  an  upper  lip,  la- 
brum  ;  an  under  lip,  labium  ;  two  pairs  of  jaws  acting  later- 
ally between  these  lips  ;  and  a  tongue-like  organ,  /lypo- 
pharynx.  The  cephalic  pair  of  jaws  is  called  the  mandibles  j 
the  caudal  pair,  the  maxillce. 

Note. — The  natural  attitude  of  the  head  of  a  locust  is  such  that  the  la- 
brum  and  lahntm  appear  to  be  fore  and  hind  lips  respectively ;  and  the 
viotuhl'h's  and  maxilltr,  fore  and  hind  pairs  of  jaws.  But  when  the  mouth 
of  an  insect  is  in  its  more  usual  position,  at  the  cephalic  end  of  the  body 
axis,  the  labrum  is  an  upper  lip,  the  labium  an  under  lip,  the  mandibles, 
the  upper  jaws,  and  the  maxillae  the  lower  jaws. 

Each  maxilla  consists  of  six  parts.  These  are  the  cardo, 
stipes,  laci/tia,  palpifer,  galea,  and  maxillary  palpus. 

The  labium  consists  of  the  submentum,  inentum,  ligula,  two 
palpigers,  and  two  labial palpt. 

THE    HEAD    OF    A    COCKROACH. 

It  is  desirable  to  supplement  the  study  of  the  head  of  a 
locust  by  an  examination  of  the  head  of  a  more  generalized 
insect ;  for  this  purpose  a  cockroach  may  be  used.  If  prac- 
ticable one  of  the  larger  species  should  be  studied. 

Make  a  drawing  of  the  ventral  aspect  of  the  head.  Owing 
to  the  difference  in  attitude  the  ventral  aspect  of  the  head 
of  a  cockroach  corresponds  to  the  cephalic  aspect  of  the 
head  of  a  locust. 


17 

Epicranial  suture. — Observe  the  inverted  Y-shaped  sut- 
ure, the  stem  of  which  is  on  the  middle  line  between  the 
compound  eyes,  and  the  arms  of  which  extend  towards  the 
antennae  ;  this  is  the  epicranial  suture. 

The  stem  of  the  epicranial  suture  divides  the  vertex  into 
two  sclerites.  The  arms  of  this  suture  separate  the  vertex 
from  the  front,  which  in  this  case  is  not  a  part  of  the  epi- 
cranium  as  it  is  in  the  locust. 

Antennal  sclerites. — Surrounding  the  base  of  each  an- 
tenna  there  is  a  more  or  less  distinct,  ring-like  sclerite  ;  this 
is  the  antennal  sclerite. 

The  antennal  sclerites  are  much  more  distinct  in  the  Plecoptera  (stone- 
flies). 

Clypeo-frontal  suture. — The  suture  separating  the  cly- 
peus  and  the  front  is  obsolete  in  the  cockroaches.  Study 
this  suture  in  the  locust,  and  note  the  relation  of  it  to  the 
point  of  articulation  of  the  mandible  with  the  clypeus  on 
each  side  ;  and  then  indicate  the  probable  position  of  it  in 
the  cockroach  by  a  faint,  dotted  line  in  your  drawing. 

Letter  the  vertex,  front,  clypeus,  labrum,  and  genje. 

Make  a  preparation  showing  the  lateral  aspect  of  the  head 
and  neck,  and  note  the  following  features  : — 

The  suture  separating  the  gena  from  the  postgena. 

The  absence  of  a  suture  separating  the  occiput  from  the 
postgena. 

An  opening  into  the  head  between  the  postgena  and  the  neck 
near  the  point  of  attachment  of  the  maxilla.  This  is  the 
mouth  of  an  invagination  of  the  body-wall  which  forms  a  part 
of  the  tentorium  ;  i.e. ,  oxi^  oi\.\\^  posterior  arms  of  the  tentorium. 

A  narrow  sclerite  bounding  the  mouth  of  this  invagination 
on  the  side  towards  the  neck  ;  this  is  one  of  the  lateral  sclerites 
of  the  tnaxillary  segment,  the  caudal  one. 

The  maxillary  segment  is  one  of  several  segments  that  enter  into  the  com- 
position of  the  head,  and  the  one  of  which  the  maxillae  are  the  appendages. 


i8 

There  are  two  sclerites  on  each  side  of  the  head  in  this  segment,  one  on  each 
side  of  the  invagination,  but  the  cephalic  one  is  so  reduced  that  it  can  be  rec- 
ognized only  with  difficulty. 

The  articulation  of  one  of  the  lateral  cervical  sclerites  with 
the  maxillary  segment. 

Make  a  drawing  of  the  lateral  aspect  of  the  head  showing 
the  features  mentioned  above. 


THE    MOUTH-PARTS   OF    THE    COCKROACH. 

In  the  cockroach  the  mouth-parts  are  very  similar  to  those 
of  the  locust  with  an  interesting  and  important  difference  in 
the  labium.  With  the  named  drawings  of  the  mouth-parts  of 
the  locust  as  guide,  the  parts  of  the  mouth  of  the  cockroach 
can  be  readily  determined  ;  the  following  brief  notes  provide 
additional  aid. 

Labrum. — Attached  to  the  margin  of  the  clypeus  as  a 
movable  cuticular  flap,  is  the  subquadrangular  labrum  or 
upper  lip,  serving  as  the  dorsal  or  anterior  covering  of  the 
mouth.  Although  the  position  and  use  of  the  labrum  makes 
it  one  of  the  mouth-parts,  it  is  morphologically  different  from 
the  other  mouth-parts  in  not  being  a  modified  appendage. 

Epipharynx. — The  epipharytix  of  all  insects  is  a  continu- 
ation or  outgrowth  of  the  upper  membranous  wall  of  the 
pharynx.  It  is,  in  the  cockroach,  as  in  most  insects  with 
biting  mouth-parts,  simply  the  ventral  or  internal  membra- 
nous wall  of  the  labrum. 

A  small  distal  portion  of  the  labrum  of  the  cockroach  is 
rather  plainly  set  off  from  the  rest  of  the  labrum  by  a  trans- 
versal suture  ;  it  may  be  that  this  distal  part  is  a  prolonga- 
tion of  the  epipharynx  alone  (a  condition  observable  among 
certain  other  insects).  When  the  labrum  and  epipharynx  are 
indistinguishably  fused  the  single  organ  is  sometimes  called 
labrum-epipharynx. 


19 

Mandibles. — Below  the  labrum-epipharynx  are  the  strong- 
ly chitinized  prominent  mandibles.  Each  mandible  is  a  single 
sclerite,  toothed  on  its  distal  or  biting  surface. 

Maxillae. — Lying  next  to  and  below  the  mandibles  are 
the  tnaxillip..  The  cardo  is  small  and  elongate,  subtriangular 
in  shape  and  divided  into  two  parts  by  a  transverse  line. 
The  stipes  is  larger,  and  subquadrangular.  Articulating  with 
the  stipes  are  the  five-segmented  maxillary  palpus,  and  the 
two  terminal  lobes,  the  galea  and  the  lacinia.  The  galea 
forms  a  sort  of  hood  for  the  smaller  triangular  lacinia  and  is 
composed  of  two  segments.  The  lacinia  ends  in  a  sharp, 
strong  chitinous  tooth.  Indications,  only,  of  the  suture  set- 
ting off  the  palpiger  can  be  discovered  in  the  maxilla  of  the 
cockroach. 

Labium. — The  labium  is  a  single  flap-like  structure,  which 
lies  below  the  maxilla,  and  forms  the  floor  of  the  mouth.  It 
is,  although  an  unpaired  organ,  really  formed  in  all  insects 
by  the  fusion  of  two  organs  similar  in  character  to  the 
maxillae.  The  labium  is  sometimes  called,  because  of  this 
homology  of  structure,  the  second  maxillae. 

In  the  cockroach  the  proximal  or  articulating  sclerite,  the 
sjibme/ituin,  is  large  and  shows  no  indication  of  its  paired 
origin.  The  succeeding  sclerite,  the  mentum,  is  smaller  and 
also  is  without  indication  of  an  original  bipartite  condition. 
Arising  from  the  mentum,  however,  are  the  two  four-seg- 
mented labial  palpi  and  four  terminal  lobes  ;  two  of  these 
lobes  and  a  palpus  belong  to  each  lateral  half  of  the  mentum 
and  correspond  to  the  lacinia,  galea,  and  palpus,  respectively, 
of  the  maxillae.  The  inner  lobes  of  the  labium  are  called 
glosscB  and  the  outer  onts,  paraglossce.  The  glossae  and  para- 
glossae  are  fused  so  that  only  their  distal  portions  are  free 
and  distinct.  This  fusion  of  the  terminal  lobes  of  the  labium 
is  carried  farther  among  most  other  insects.  Often  the 
paraglossa  and  glossa  of  each  side  will  fuse  completely  so 


20 

that  there  are  apparently  but  two  terminal  lobes,  and  these 
distinct  only  distally,  or  all  of  the  terminal  lobes  may  fuse  to 
form  a  simple  flap-like  sclerite,  as  among  some  of  the  Neu- 
roptera.  Because  of  this  fusing  of  the  bases  or  of  all  of  the 
terminal  lobes  they  are  often  spoken  of  collectively  as  the 
ligula  (see  p.  14.  in  account  of  external  anatomy  of  the 
locust). 

Hypopharynx. — The  hypopharynx  is  a  fleshy,  blunt- 
pointed,  tongue-like  lobe,  supported  by  a  chitinized  frame- 
work ;  this  chitinous  framework  at  the  basal  part  of  the 
hypopharynx  projects  backwards  as  four  slender  rods,  two 
dorsal  and  two  ventral,  the  ventral  ones  being  curved  and 
shorter  than  the  upper.  This  chitinous  framework  is  called 
the  pharyngeal  skeleton. 

Make  drawings  of  all  the  mouth-parts  of  the  cockroach, 
naming  the  sclerites. 

Cervical  sclerites. — Study  the  neck  of  the  cockroach 
and  note  that  there  are  eight  cervical  sclerites,  two  dorsal, 
two  ventral  and  two  on  each  lateral  aspect. 

THE    PARTS    OF    THE    THORAX. 

Division  into  segments. — Return  to  the  study  of  the 
locust.  The  thorax  consists  of  three  segments.  The  cephalic 
or  first  segment  is  named  \.\\t  prothorax ;  the  second  or  inter- 
mediate, the  mesothorax  J  and  the  third  or  caudal,  the  met- 
athorax. 

These  divisions  of  the  thorax  can  be  easily  recognized  by 
the  appendages  they  bear.  To  the  prothorax  is  articulated 
the  first  pair  of  legs  ;  to  the  mesothorax  are  joined  the  sec- 
ond pair  of  legs  and  the  first  pair  of  wings  ;  and  to  the 
metathorax,  the  third  pair  of  legs  and  the  second  pair  of 
wings. 


21 


PROTHORAX, 


Dorsal  part  (pronotum). — That  which  may  be  properly 
termed  the  dorsal  part  of  the  prothorax  is  a  large  sunbon- 
net-shaped  piece  which  covers  the  greater  portion  of  the 
sides  as  well  as  the  dorsal  surface  of  this  segment.  This 
piece  is  called  the  prono^uvi. 

It  is  believed  that  the  dorsal  part  of  each  thoracic  segment 
consists  typically  of  four  sclerites.  These  are  named,  be- 
ginning with  the  cephalic,  prcescidtim,  scutum,  scutellum,  and 
postscutellum.  These  sclerites  may  be  distinguished  in  the 
dorsal  parts  of  the  mesothorax  and  metathorax  [luesonotuni 
and  mctanotum)  of  many  insects ;  but  the  pronotum  consists 
usually  of  a  single  piece.  In  the  insect  which  we  are  study- 
ing, although  the  pronotum  consists  of  a  single  piece,  it  is 
crossed  by  three  well-marked  sutures,  indicating  the  di- 
vision into  four  sclerites,  which  may  be  named  as  indicated 
above. 

On  the  latero-dorsal  aspect  of  the  pronotum  the  suture 
between  the  praescutum  and  the  scutum  extends  cephalad 
for  a  short  distance  and  is  then  interrupted  ;  the  lateral  por. 
tion  of  this  suture  is  parallel  with  and  quite  near  to  the 
cephalic  margin  of  the  pronotum.  Near  the  center  of  each 
lateral  aspect  of  the  pronotum  there  is  a  short  oblique  suture 
which  separates  the  lateral  fourth  of  the  scutellum  from  the 
mesal  part  of  that  sclerite.  None  of  the  sutures  extend  to 
the  lateral  margin  of  the  pronotum, 

Make  a  drawing  of  the  lateral  aspect  of  the  pronotum. 

Ventral  part. — The  ventral  part  of  each  thoracic  seg- 
ment consists  typically  of  two  sclerites,  one  situated  in  front 
of  the  other  ;  the  first  is  the  sternum,  the  second,  which  has 
never  been  named,  may  be  termed  the  sternellum.  The 
sternellum  is  frequently  divided  longitudinally  into  two 
parts,  which  may  be  widely  separated. 


22 

Prosternum. — On  the  ventral  surface  of  this  segment 
between  the  legs  there  is  a  sclerite  which  bears  a  large 
tubercle  ;  this  is  the  sternum  of  the  prothorax  ox  prosternum. 

P roster nellum. — The  sternellum  of  the  prothorax,  or  the 
prosternellum,  is  a  narrow,  transverse  sclerite,  which  is  close- 
ly united  to  the  following  segment. 

Lateral  parts. — Owing  to  the  great  development  of  the 
pronotum,  which  covers  the  larger  portion  of  the  sides  as 
well  as  the  dorsal  surface  of  the  prothorax,  the  lateral  parts 
of  this  segment  are  rudimentary.  The  following  named 
sclerite,  however,  may  be  distinguished. 

Episternian. — Between  the  pronotum  and  the  end  of  the 
lateral  prolongation  of  the  prosternum,  which  extends  on 
each  side  of  the  segment  cephalad  of  the  leg,  is  a  conspicu- 
ous triangular  sclerite  ;  this  is  the  episternum. 

Add  the  episternum  to  the  drawing  of  the  lateral  aspect  of 
the  pronotum, 

MESOTHORAX    AND    METATHORAX. 

Union  of  these  segments.  —  The  second  and  third 
thoracic  segments  are  firmly  joined  together,  forming  a  box 
to  which  the  two  pair  of  wings  and  the  second  and  thiVd 
pairs  of  legs  are  joined.  Owing  to  the  intimate  union  of 
these  two  segments  it  wnl  be  easier  to  describe  them  together 
than  separately. 

With  fine  pointed  scissors  cut  away  the  caudal  border  of 
the  pronotum,  that  part  which  overlaps  the  mesonotum  ;  be 
careful  not  to  break  the  membrane  connecting  the  protho- 
rax and  mesothorax. 

Dorsal  part  (mesonotum  and  metanotum).  —  The 
dorsal  part  of  the  mesothorax  is  termed  the  mesonotum,  that  of 
the  metathorax,  the  metanotum.  Unlike  the  pronotum  these 
parts  are  confined  to  the  dorsal  aspect  of  the  body.     By  cut- 


23 

ting  away  the  caudal  part  of  the  pronotum  as  indicated  above 
and  spreading  the  wings  laterad,  these  parts  are  exposed. 
Each  consists  of  a  nearly  square  area.  To  the  lateral  mar- 
gins of  the  mesonotum  is  articulated  the  first  pair  of  wings  ; 
and  to  the  lateral  margins  of  the  metanotum,  the  second  pair 
of  wings. 

The  sutures  indicating  the  outlines  of  the  sclerites  of 
which  the  mesonotum  and  metanotum  are  composed,  are  not 
well  defined  ;  there  is  consequently  some  difficulty  in  deter- 
mining the  limits  of  the  sclerites  ;  and  a  drawing  of  this  part 
will  not  be  required. 

In  each  of  these  segments  only  two  of  the  four  dorsal 
sclerites  are  well  developed  ;  these  are  the  scutum  and  the 
scutellum.  The  scutum  occupies  the  cephalic  half  of  the  seg- 
ment, the  scutellum  the  caudal  half.  The  scutellum  consists 
of  three  parts  :  a  central,  shield-shaped  part,  which  in  this 
species  is  closely  united  to  the  scutum  ;  and  on  each  side  a 
part  extending  to  the  base  of  the  wing.  The  caudal  border 
of  the  scutellum  is  thickened  and  is  connected  on  each  side 
with  the  caudal  border  of  the  base  of  the  wing  by  a  cord-like 
structure. 

Note. — In  those  insects  where  the  prsescutum  and  postscutellum  are  well 
developed,  they  usually  extend  entad  and  are  often  concealed  within  the 
thorax.  The  connection  of  the  scutellum  on  each  side  with  the  caudal  bor- 
der of  the  base  of  the  wing,  is  an  excellent  guide  in  tracing  the  homology  of 
the  parts  of  the  mesonotum  and  the  metanotum. 

Ventral  part. — On  the  ventral  surface  of  the  body  be- 
tween the  legs  of  the  second  thoracic  segment  is  a  large 
sclerite  ;  this  is  the  sternum  and  the  sternellum  of  the  meso- 
thorax  combined.  The  cephalic  margin  of  this  sclerite  is 
nearly  straight  ;  the  caudal  margin,  deeply  notched  by  a 
large,  nearly  square  incision.  The  part  in  front  of  this 
notch  is  the  sternum  of  the  mesothorax  or  niesosternum,  the 
two  parts,  one  on  each  side  of  this  notch,  are  the  widely  sep- 


24 

arated  halves  of  the  sternellum  of  the  mesothorax  or  meso^ 
sterncllum. 

Caudad  of  the  mesosternum  and  mesosternellum  there  is  a 
large  sclerite,  the  mesal  part  of  which  is  prolonged  cephalad  so 
as  to  accurately  fit  the  notch  in  the  caudal  border  of  the  meso- 
thorax ;  this  is  the  sternum  of  the  metathorax  or  metasternum. 

The  two  halves  of  the  sternellum  of  the  metathorax,  or 
metasternelluvi,  are  widely  separated,  each  being  situated  near 
the  base  of  the  corresponding  leg. 

The  caudal  border  of  the  metathorax  is  also  notched,  and 
the  first  abdominal  segment  is  dove-tailed  into  it. 

Cephalad  of  the  base  of  each  mesothoracic  and  meta- 
thoracic  leg  there  is  a  crescent-shaped  sclerite  ;  this  is  the 
antecoxal  piece. 

Make  a  drawing  of  these  parts. 

Lateral  parts  (episterna,  epimera,  and  peritremes). 
— Examine  one  side  of  the  second  and  third  thoracic  seg- 
ments. Note  that  it  is  chiefly  composed  of  four  large  scle- 
rites,  which  extend  from  the  fossae  of  the  legs  dorsocephalad. 
These  sclerites  are  named  as  follows  : — 

Epister7ium  of  the  mesothorax. — The  first  or  cephalic  of 
these  four  sclerites  is  the  episterimm  of  the  mesothorax.  The 
sutures  between  the  episterna  and  the  mesosternum  are  only 
faintly  indicated  in  this  species. 

Epimeron  of  the  mesothorax. — This  is  the  second  of  this 
series  of  sclerites. 

Episterniim  of  the  metathorax. — This  is  the  third  of  this 
series  of  sclerites  ;  it  is  the  one  which  bears  the  oblique 
yellow  band  characteristic  of  this  species. 

Epimeron  of  the  metathorax. — This  is  the  caudal  member 
of  this  series  of  sclerites. 

Spiracles  and  peritremes. — Between  the  ventro-caudal  angle 
of  the  epimeron  of  the  mesothorax  and  the  fossa  of  the  leg 
is  an  organ  which  consists  of  a  slit-like  opening  guarded  by 


25 

two  fleshy  lips  ;  this  is  one  of  the  openings  of  the  respira- 
tory system  ,  these  openings  are  called  spiracles.  When,  as 
in  this  case,  a  spiracle  is  surrounded  by  a  circular  sclerite, 
such  a  sclerite  is  termed  ^.peritreme. 

In  the  membrane  connecting  the  mesothorax  with  the  pro- 
thorax  there  is  on  each  side  a  spiracle.  This  spiracle  is 
covered  by  the  free  margin  of  the  pronotum.  In  this  case 
the  peritreme  is  developed  on  the  ventral  side  of  the  spiracle 
into  a  prominent  papilla. 

Make  a  drawing  of  the  lateral  parts  of  the  mesothorax  and 
metathorax. 

Review. — The  thorax  consists  of  three  segments,  which 
are  named,  beginning  with  the  ct^thSiWc,  p  rot  ho  rax,  mesothorax, 
and  metathorax. 

The  body-wall  of  each  of  these  segments  is  believed  to 
consist  typically  of  ten  sclerites.  Of  these,/i?z/r  pertain  to  the 
dorsal  part  of  the  segment ;  tivo  to  each  lateral  part ;  and  tiuo 
to  the  ventral  part. 

The  dorsal  sclerites  are  named,  beginning  with  the  ceph- 
alic, pr(zscutum,  scutum,  scutellum,  and  postscutellum. 

Of  the  lateral  sclerites,  the  cephalo-ventral  one  is  the  epi- 
sternum,  the  caudo-dorsal  one,  the  epimeron 

The  ventral  sclerites  are  known  as  the  sternum  and  the 
sternellum.  The  sterna  of  the  three  thoracic  segments  are 
designated  as  the  prosternum,  mesosternum,  and  metasternum 
respectively;  and  the  sternella  as  iht  prosternellum,  mesoster- 
nellum,  and  metasternelluin. 

In  most  insects  the  sternella  are  so  reduced  in  size  as  to 
be  indistinguishable. 

Sometimes  there  is  also  present  near  the  base  of  the  leg  a 
distinct  antecoxal piece 

The  dorsal  part  of  the  body-wall  of  each  segment  is  called 
the  tergum.  This  name  is  also  applied  to  the  dorsal  part  of 
the  three  thoracic  segments  collectively. 


l\ 


9-1 


26 

The  tergum  of  the  prothorax  is  frequently  called  \.\\t  pro- 
?iotum ;  the  tergum  of  the  mesothorax,  the  tnesonotutn  j  and 
that  of  the  metathorax,  the  metanotum. 

There  are  in  this  insect  two  pairs  of  thoracic  spiracles. 

APPENDAGES,  OF    THE    THORAX. 

The  appendages  of  the  thorax  are  the  legs  and  the  wings  ; 
the  number  and  distribution  of  these  have  already  been  given. 

Legs. — Examine  the  ventral  aspect  of  the  first  pair  of 
legs.  Each  leg  will  be  found  to  consist  of  the  following 
named  parts  . — 

Coxa. — This  is  the  proximal  segment  of  the  leg.  It  is  sub- 
globular  in  outline.  Examine  the  cephalic  aspect  of  the  coxa, 
and  note  the  longitudinal  suture  which  traverses  this  side  of 
it ;  this  is  shown  better  on  the  mesothoracic  legs. 

Trochanter. — This  is  the  second  segment  of  the  leg,  and  is 
much  smaller  than  the  coxa.  The  ventral  aspect  of  it  is 
much  longer  than  the  dorsal. 

Femur. — This  is  the  third  and  principal  segment  of  the 
leg. 

Tibia. — This  is  the  fourth  segment  of  the  leg.  It  nearly 
equals  the  femur  in  length,  but  is  more  slender. 

Tarsus. — The  tarsus  include-s  all  of  that  part  of  the  leg 
distad  of  the  tibia.     It  consists  in  locusts  of  three  segments. 

The  last  segment  of  the  tarsus  bears  a  pair  of  claws. 

On  the  ventral  surface  of  the  tarsus  there  is  a  series  of 
cushions  ,  these  are  called  pulvilli.  The  distal  segment  of 
the  tarsus  bears  a  single  pulvillus  which  projects  between 
the  claws  ,  this  is  often  referred  to  in  descriptive  works  as 
the  pulvillus. 

Note. — In  the  membrane  connecting  the  coxa  with  the  thorax  just  ceph- 
alad  of  the  coxa,  is  a  sclerite ,  this  we  beheve  to  be  the  trochantin  The 
trochantin  is  a  sclerite  which  is  considered  to  be  an  appendage  of  the  coxa, 
and  its  normal  position  is  between  the  coxa  and  the  antecoxal  piece 


27 

Make  a  drawing  of  one  of  the  cephalic  legs. 

The  same  parts  may  be  traced  on  each  of  the  other  legs. 

Winga. — The  wings  are  plate-like  or  membraneous  ex- 
pansions of  the  body-wall.  Each  wing  is  traversed  by  many 
linear  thickened  portions  ;  these  are  termed  veins  or  nerves. 
The  principal  veins  extend  proximo-distad.  These  are  joined 
together  by  many  smaller  cross-veins.  The  thin  parts  cir- 
cumscribed by  the  veins  and  cross-veins  are  called  cells. 

The  two  pairs  of  wings  of  a  locust  differ  remarkably  in 
form  and  texture. 

Mesothoracic  wings  {tegmina). — The  mesothoracic  wings  are 
long,  narrow,  and  of  a  parchment-like  texture.  They  are 
termed  tegmina. 

Metathoracic  wings. — The  metathoracic  wings  are  much 
larger  and  of  more  delicate  texture  than  the  first  pair  of 
wings.  When  not  in  use  they  are  folded  in  plaits  like  a  fan 
and  concealed  by  the  tegmina.  Some  writers  who  designate 
the  mesothoracic  wings  as  tegmina  or  wing-covers,  describe 
the  metathoracic  wings  simply  as  the  wings. 

PARTS    OF    THE    ABDOMEN. 

Number  of  segments  — There  is  a  difference  of  opinion 
as  to  the  number  of  segments  in  the  body  of  a  locust.  The 
difficulty- arises  from  the  complexity  of  the  caudal  end  of 
this  region,  and  the  fact  that  some  authors  have  considered 
the  first  abdominal  sternum  as  a  part  of  the  metathorax. 
Eight  abdominal  segments  can  be  readily  distinguished  in 
the  female  ,  and  nine,  in  the  male.*  Caudad  of  the  eighth 
abdominal  segment  of  the  female  and  the  ninth  of  the  male 

*If  a  sufficiently  large  series  of  specimens  of  the  red-legged  locusts  be  e.vam- 
ined  it  will  be  seen  that  there  are  two  kinds  ,  one,  m  which  the  caudal  part  of 
the  body  tapers  to  the  end,  and  bears  four,  pointed  and  curved,  horny  pieces  ; 
and  another,  in  which  the  caudal  part  of  the  body  increases  in  size  caudad 
and  is  terminated  by  a  single,  large,  hood-shaped  plate.  The  former  is  the 
female  ,  the  latter,  the  male. 


28 

are  a  number  of  sclerites  which  are  considered  by  some 
writers  to  be  merely  appendages  of  the  abdomen  ;  other 
writers  hold  that  certain  of  these  sclerites  represent  sterna; 
and  certain  others,  terga. 

It  is  not  within  the  scope  of  this  work  to  enter  into  any 
discussion  of  the  matter.  We  shall  describe  the  parts  as  if 
there  were  eleven  segments  ;  but  wish  the  student  to  under- 
stand that  the  so-called  eleventh  segment  may  be  merely  an 
appendage  of  the  tenth  ;  and  that  what  is  described  here  as 
the  ninth  and  tenth  segments  have  not  been  considered  as 
such  by  certain  very  high  authorities. 

First  abdominal  segment — The  dorsal  and  ventral 
parts  of  the  first  abdominal  segment  are  widely  separated  by 
the  caudal  part  of  the  cavities  for  the  insertion  of  the  third 
pair  of  legs. 

The  ventral  part  of  this  segment  is  dove-tailed  into  the 
metasternum,  and  at  first  sight  would  be  taken  for  a  part  of 
the  thorax. 

On  each  side  in  the  dorso-lateral  part  of  this  segment, 
there  is  a  large  opening  which  is  closed  by  a  very  delicate 
membrane  ;  these  are  >he  auditory  organs  ;  the  membrane  is 
the  tympajium. 

Just  cephalad  of  each  auditory  organ  there  is  a  small 
opening  ;  these  are  the  first  pair  of  abdominal  spiracles. 

Second  to  eighth  abdominal  segments.— Each  of 
the  abdominal  segments,  from  the  second  to  the  eighth  in- 
clusive, is  ring-like  in  form,  and  without  appendages. 

In  each  of  these  segments  the  lateral  margins  of  the  ter- 
gum  join  the  pleura  *  without  any  suture.     Near  the  cepha- 

*The  lateral  part  of  a  segment  is  termed  the  pleurum  ;  in  the  same  way  that 
the  ventral  part  is  called  the  sternum;  and  the  dorsal  part,  the  tcrgum.  By 
some  writers  the  entire  dorsal  part  ol  an  insect  is  called  the  tergum  ,  the  lateral 
part,  the  pleurum  ;  and  the  ventral  part,  the  sternum.  These  writers  apply  the 
terms  tergite,  pleurite,  and  sternite  respectively,  to  the  dorsal,  lateral,  and  ster- 
nal regions  of  each  segment. 


29 

lo-ventral  angle  of  each  pleurum  there  is  a  spiracle.  The 
sterna  are  well  developed  and  are  separated  from  the  pleura 
by  a  narrow,  involuted,  membraneous  part. 

Caudal  part  of  abdomen  of  female. — The  most  promi- 
nent portion  of  the  caudal  part  of  the  abdomen  of  the 
female  is  the  ovipositor.  This  is  an  organ  consisting  of  four, 
strong,  curved,  and  pointed  pieces,  which  form  the  most 
caudal  part  of  the  body.  With  this  organ  the  insect  makes  a 
hole  in  the  ground  in  which  she  lays  her  eggs.  This  is  done 
by  alternately  bringing  together  and  separating  the  two  pairs 
of  pieces,  and  at  the  same  time  pushing  the  body  into  the 
ground.  Examine  carefully  these  pieces,  and  note  how  well 
they  are  adapted  to  this  purpose. 

Between  the  ventral  pieces  is  the  opening  of  the  oviduct. 

Ventrad  of  this  opening  and  also  between  the  ventral 
pieces  of  the  ovipositor  is  a  pointed  prolongation  of  the 
eighth  abdominal  sternum  ;  this  has  been  termed  the  egg- 
guide.  Dorsad  of  the  egg-guide  there  is  a  forked  organ 
which  also  is  used  in  placing  the  eggs. 

The  ventral  pieces  of  the  ovipositor  are  supported  by  two 
pairs  of  sclerites  ;  there  being  a  sclerite  closely  applied  to 
the  ventral  surface  of  each  pair,  and  one  to  the  lateral  sur- 
face of  each. 

The  ninth  and  tenth  abdominal  terga  are  shorter  than  any 
of  the  preceding  abdominal  terga  and  are  joined  together  on 
each  side,  the  lateral  parts  of  the  suture  separating  them 
being  obsolete. 

Caudad  of  the  tenth  tergum  there  is  on  the  middle  of  the 
back  a  shield-shaped  piece  ;  this  is  believed  to  represent  an 
eleventh  segment.  It  consists  of  two  sclerites,  as  is  indi- 
cated by  a  transverse  suture. 

On  each  side,  projecting  from  beneath  the  caudal  border 
of  the  tenth  tergum,  is  a  pointed  appendage  •  these  are  the 
cerci. 


30 

Each  cercus  partially  covers  a  much  larger,  triangular 
sclerite  which  extends  from  the  lateral  border  of  the  tenth 
tergum  to  the  caudal  apex  of  the  eleventh  tergum  ;  these  are 
the  podical  plates. 

By  lifting  the  free  end  of  the  eleventh  segment,  the  cau- 
dal opening  of  the  alimentary  canal,  the  anus,  is  exposed  ;  it 
is  situated  between  the  podical  plates. 

Caudad  of  the  podical  plates  is  the  dorsal  pair  of  pieces  of 
the  ovipositor. 

Make  drawings  of  the  dorsal  and  the  lateral  aspects  of  this 
part  of  the  body  ;  in  the  drawing  of  the  lateral  aspect  repre- 
sent the  entire  abdomen. 

Caudal  part  of  the  abdomen  of  the  male.— In  the 
male  ten  abdominal  sterna  are  present  ;  the  tenth  is  a  hood- 
shaped  sclerite  on  the  caudal  aspect  of  the  body. 

As  in  the  female,  the  ninth  and  tenth  abdominal  terga  are 
united  on  their  lateral  margins. 

Projecting  from  the  caudal  margin  of  the  tenth  tergum 
there  is  on  the  middle  of  the  back  a  forked  appendage,  the 
fur  cilia. 

The  eleventh  tergum  is  furrowed  by  three  deep  longitu- 
dinal grooves. 

The  cerci  are  situated  as  in  the  female,  but  are  longer. 

The  podical  plates  are  nearly  as  in  the  female. 

Make  drawings  of  the  dorsal  and  the  lateral  aspects  of 
this  part  of  the  body. 


CHAPTER   III. 

THE   INTERNAL  ANATOMY   OF  AN   INSECT. 
Corydalis  cornuta. 

The  larva  of  Corydalis  cornuta  lives  under  stones  in  the  bed 
of  swiftly  flowing  streams  ;  it  is  well  known  to  sportsmen 
under  the  name  of  "  dobson,"  and  is  used  extensively  as  bait 
for  black  bass. 

As  the  larval  state  of  Corydalis  lasts  nearly  three  years, 
larvae  which  are  at  least  two  years  old  may  be  found  at  any 
time.  They  are  most  abundant  where  the  water  flows  swift- 
est. A  good  way  to  obtain  them  is  to  hold  a  dip-net  or  a 
wire  screen  in  the  stream  below  some  stones,  and,  lifting  the 
stones  with  a  hoe  or  garden  rake,  cause  the  current  to  sweep 
into  the  net  the  insects  which  were  under  the  stones. 

This  larva  is  probably  as  desirable  a  subject  for  an  ele- 
mentary study  of  the  internal  anatomy  of  insects  as  ,can  be 
found  in  this  country.  The  species  is  a  large  one,  being  one 
of  our  largest  insects  ;  there  is  a  coarseness  in  its  structure, 
which  enables  one  to  study  the  different  viscera  with  com- 
parative ease  ;  it  is  furnished  with  well-developed  organs  for 
aquatic  respiration,  and  at  the  same  time  with  equally  well- 
developed  organs  for  aerial  respiration ;  and,  as  already 
stated,  fresh  specimens  can  be  easily  obtained  at  any  season, 
even  in  mid-winter. 

Unfortunately,  however,  the  appearance  of  the  insect  is 
very  disagreeable  to  most  people.  But  after  a  specimen  has 
been  opened  and  pinned  upon  cork,  as  is  necessary  in  the 
study  of  the  viscera,  the  disagreeable  features  are  not  visible  ; 

31 


32 

and  the  ease  with  which  the  internal  organs  can  be  examined 
more  than  counterbalances  the  unpleasant  part  of  the  prepara- 
tion of  specimens. 

PRESERVATION    OF    SPECIMENS. 

Specimens  that  are  to  be  used  for  the  study  of  internal 
anatomy  should  be  preserved  in  an  aqueous  solution  of  chlo- 
ral hydrate  ;  this  is  made  by  dissolving  one  part  by  weight  of 
chloral  hydrate  in  twenty  parts  of  water.  This  liquid  pre- 
serves the  organs  and  at  the  same  time  leaves  them  flexible. 
After  the  specimens  have  been  in  the  solution  for  one  day,  a 
short,  longitudinal  slit  must  be  made  through  the  wall  of  the 
abdomen,  so  as  to  allow  the  solution  to  enter  the  perivisceral 
cavity  ;  otherwise  the  viscera  will  decay.  The  delay  of  one 
day  before  making  the  slit  in  the  body  is  important ;  if  the 
slit  is  made  too  soon,  the  muscles  will  contract  in  such  a  way 
as  to  distort  the  specimen  and  render  it  worthless.  One-half 
of  the  specimens  should  be  slit  on  the  back,  the  others,  on 
the  ventral  side  ;  for  if  the  specimens  are  all  cut  in  the  same 
manner,  it  will  be  impracticable  to  study  certain  organs. 

If  a  very  careful  study  is  to  be  made  of  the  external  anat- 
omy of  this  larva,  one  or  more  specimens  should  be  left  for 
several  days  in  a  warm  place,  in  the  chloral  hydrate  solution, 
without  being  cut.  The  parts  bathed  by  the  solution  will  be 
well-preserved  ;  the  viscera  will  decay  ;  and  the  gases  of  de- 
composition will  so  distend  the  body  that  the  different  scle- 
rites  will  be  spread  apart. 

EXTERNAL    CHARACTERISTICS. 

In  order  to  understand  the  internal  anatomy  of  this  insect 
it  is  necessary  to  know  the  more  general  features  of  its  ex- 
ternal anatomy.  We  will  not  stop  to  trace  out  the  homol- 
ogies of  the  different  sclerites  which  enter  into  the  compo- 


33 

sition  of  the  body-wall,  but  will  merely  examine  the  more 
important  external  structures. 

Pin  a  larva  to  the  cork  or  beeswax  lining  of  a  dissecting 
dish,  with  its  ventral  aspect  uppermost,  and  cover  it  with 
water.  Make  a  drawing  of  the  ventral  surface.  Name  the 
regions  and  the  appendages  of  the  body  shown  in  this  view. 
The  long,  tapering  appendages  on  the  margins  of  the  abdo- 
men may  be  termed  the  lateral  filaments  ;  the  tufts  of  hair — 
like  appendages  near  the  bases  of  the  lateral  filaments  are 
.tracheal  gills ;  and  caudad  of  the  ninth  abdominal  segment 
is  a  pair  of  pfolegs.  These  may  be  termed  the  anal  pro- 
legs.^ 

Make  a  drawing  of  each  of  the  following  parts  : — 

1.  The  dorsal  aspect  of  the  head,  showing  the  mandibles, 
the  antennae,  and  the  labrum. 

2.  One  of  the  tracheal  gills.  Cut  off  several  of  the  hair- 
like branches  and  mount  them  in  glycerine,  using  a  thin 
cover-glass.  Examine  them  with  a  compound  microscope, 
using  a  high  power.  The  surface  of  each  hair  is  marked 
with  numerous  ridges,  which  resemble  in  appearance  the  fine 
ridges  on  the  skin  of  the  palm  of  the  human  hand.  In  the 
center  of  each  hair,  and  extending  nearly  its  entire  length,  is 
a  large  tube.  This  is  a  trachea  or  air  vessel.  Tracheae  can 
be  distinguished  from  other  vessels  by  being  marked  with 
transverse  lines,  which  occur  at  regular  and  very  short  inter- 
vals. The  intimate  structure  of  tiie  tracheae  will  be  studied 
later  ;  but  at  this  point  the  student  should  become  familiar 
with  the  appearance  of  tracheae,  so  that  when  he  dissects  the 
insect  he  can  readily  distinguish  them  from  other  vessels. 
Branching  from  this  large  central  trachea  are  numerous  very 

*  Many  larvae  bear  upon  the  abdomen  locomotive  appendages,  which  resem- 
ble legs,  and  are  termed  prolegs.  This  is  especially  true  t)f  caterpillars,  which 
bear  from  one  to  five  pairs  of  these  appendages.  The  prolegs  are  temporary 
organs,  being  shed  with  the  skin  when  the  larva  transforms  to  a  pupa. 


34 

small  trache?e.     Carefully  trace  out  the  courses  of  the  small 
tracheae  and  represent  them  in  your  dravvuig. 
3,  A  spiracle. 

INTERNAL    ANATOMY. 

Preliminary  work. —  Take  from  the  chloral  hydrate 
solution  a  specimen  which  was  slit  on  the  ventral  surface. 
Immerse  the  insect  in  water,  with  its  dorsal  surfac-e  down- 
wards. With  fine  scissors  extend  the  slit  the  whole  length 
of  the  thorax  and  abdomen  ;  in  making  this  slit  cut  through 
the  wall  of  the  body  into  the  perivisceral  cavity  ;  the  body- 
wall  consists  of  two  parts,  the  external  crust  of  the  insect, 
and,  entad  of  this  a  wall  of  muscles ;  it  requires  consider- 
able care  to  cut  into  the  perivisceral  cavity  and  not  injure 
the  viscera.  Make,  on  each  side,  in  that  part  of  the  body- 
wall  connecting  the  prothorax  with  the  head,  an  incision 
extending  from  the  longitudinal  incision  to  the  side  of  the 
body. 

On  the  meson  just  entad  of  the  ventral  wall  of  the  body, 
there  are  two  white  cords,  extending  nearly  the  whole 
length  of  the  body.  At  intervals,  which  approximate  the 
segments  in  length,  these  cords  are  united  ;  at  the  points  of 
union  they  are  greatly  enlarged  ;  from  these  enlargements 
there  arise  numerous,  small,  white  cords,  which  extend  in 
various  directions.  The  two  longitudinal  cords,  the  en- 
largements upon  them,  and  the  numerous  cords  branching 
from  these  enlargements  constitute  the  nervous  system ;  the 
cords  are  nerves  and  the  enlargements  are  ganglia.  The 
nervous  system  will  be  studied  later  in  a  specimen  which 
has  been  opened  on  the  dorsal  side. 

Cut  away  from  the  ganglia  the  nerves  that  extend  to  one 
side  ;  do  this  with  the  scissors,  first  placing  one  blade  under 
the  nerves  and  lifting  them  away  from  the  other  viscera. 

Take  a  strip  of  sheet-cork  a  little  longer  than  the  insect 


35 

and  twice  as  wide,  and  pin  it  to  the  beeswax  lining  of  the 
dissecting  dish,  and  cover  it  deeply  with  water.  Place  the 
specimen  on  the  cork  and  fasten  with  a  pin  at  each  end. 
Turn  laterad  each  half  of  the  ventral  wall  and  pin  it  down  to 
the  cork,  using  ribbon-pins. 

Note. — At  the  close  of  the  day's  work  on  this  subject  the  student  should 
remove  the  strip  of  cork  from  the  dissecting  dish  and  place  it  with  the  speci- 
men still  spread  out  upon  it  in  a  wide-mouthed  bottle  of  chloral  hydrate 
solution.  By  doing  this  the  work  can  be  resumed  without  the  necessity  of 
making  a  new  dissection. 

Ramifying  through  all  parts  of  the  body  are  numerous 
trachea  ;  the  larger  tracheae  are  of  a  dusky  color  ;  but  many 
of  the  smaller  ones  contain  air,  which  renders  them  silvery 
white.  On  each  side  of  the  body,  extending  the  entire 
length  of  the  thorax,  are  two  very  large  tracheae  ;  from  each 
side  of  each  abdominal  segment  except  the  last  there  arises 
a  large  trachea,  which  divides  and  subdivides  into  numerous 
branches.  Cut  a  short  piece  from  one  of  the  large  abdom- 
inal tracheae,  examine  it  with  a  compound  microscope,  and 
note  its  characteristic  appearance,  so  as  to  be  able  to  distin- 
guish tracheae. 

In  the  dissection  of  this  specimen,  the  student  may  cut 
tracheae  and  nerves  freely  ;  but  great  care  should  be  used 
not  to  cut  other  vessels  unless  specially  directed  to  do  so. 

In  the  center  of  the  perivisceral  cavity  and  extending  the 
whole  length  of  the  body,  there  is  a  large  tube  ;  this  is  the 
alimentary  canal. 

Adipose  tissue. — Surrounding  the  caudal  half  of  the 
alimentary  canal  and  attached  to  the  lateral  and  dorsal  walls 
of  the  abdomen  and  thorax,  there  are  large,  flocculent 
masses  of  a  white  substance  ;  this  is  the  adipose  tissue  or  fat. 

Examine  a  preparation  of  adipose  tissue,  with  a  compound 
microscope,  using  a  high  power,  and  make  a  drawing  show- 
ing the  minute  structure  of  the  tissue. 


36 

In  the  farther  dissection  of  this  specimen  the  adipose 
tissue  may  be  cut  away  when  necessary  to  see  the  parts 
studied. 

Form  of  the  alimentary  canal. — Remove  the  ventral 
wall  of  the  head  so  as  to  expose  the  alimentary  canal 
throughout  its  entire  length. 

Make  a  drawing  of  the  alimentary  canal  and  label  the  fol- 
lowing parts  : — 

Pharynx. — The  somewhat  trumpet-shaped  part  of  the 
alimentary  canal  immediately  caudad  of  the  mouth  is  the 
pharynx. 

(Esophagus. — That  part  of  the  alimentary  canal  which  is 
immediately  caudad  of  the  pharynx  and  which  traverses  the 
caudal  part  of  the  head  and  the  cephalic  part  of  the  thorax 
is  the  (esophagus.  It  is  a  straight  tube  of  nearly  uniform 
diameter  except  when  some  portion  of  it  is  distended  by 
food. 

Proventriculus. — In  the  caudal  part  of  the  thorax  the 
alimentary  canal  begins  to  enlarge.  This  enlargement  in- 
creases gradually  caudad  until,  in  the  first  or  second  abdom- 
inal segment,  its  diameter  is  twice  that  of  the  oesophagus  ; 
then  it  contracts  quite  suddenly  until  its  diameter  is  less 
than  that  of  the  oesophagus  ;  this  enlarged  portion  is  the 
proventriculus.  It  corresponds  in  function  with  the  gizzard 
of  birds  and  is  very  complicated  in  structure  internally. 

Ventriculus. — Caudad  of  the  constriction  following  the  pro- 
ventriculus, there  is  a  slightly  enlarged  portion,  from  the 
cephalic  end  of  which  there  project  cephalad,  four  large 
pouches ;  this  enlargement  is  the  ventriculus  or  stomach  and 
the  pouches  are  the  gastric  cceca.  The  two  caeca  of  each 
side  are  quite  closely  united. 

Malpighian  vessels. — Emptying  into  the  caudal  end  of  the 
ventriculus  are  several,  small,  very  long,  and  much  convo- 
luted  tubes  ;  these  are  the   Malpighian  vessels ;   they   were 


37 

named  in  honor  of  Malpighi,  one  of  the  early  anatomists. 
As  uric  acid  is  found  in  the  Malpighian  vessels,  they  are 
supposed  to  correspond  to  the  kidneys  in  function. 

Determine  the  number  of  Malpighian  vessels. 

Intestine. — The  part  of  the  alimentary  canal  extending  from 
the  ventriculus  to  the  caudal  end  of  the  body  is  the  intes- 
tine ;  the  part  immediately  caudad  of  the  ventriculus  is  the 
small  inte stifle  J  following  the  small  intestine  is  the  large 
intestine  J  there  are  two  bends  in  the  cephalic  part  of  the 
large  intestine  ;  the  first  extends  dorsad  and  cephalad  ;  the 
second,  dorsad  and  caudad  ;  the  rectum  is  not  a  well-defined 
part  of  the  intestine  in  this  insect. 

Attachments  of  the  alimentary  canal.  —  The  alimentary  canal  is 
attached  to  the  body-wall  and  thus  held  in  place  in  various  ways.  The 
most  obvious  attachments  are  those  of  the  ends  of  this  organ.  In  addition 
to  these  direct  connections,  the  alimentary  canal  is  indirectly  connected  to 
the  body-wall  as  follows :  — 

By  trachea. — From  the  lateral  wall  of  each  abdominal  segment,  large 
tracheae  arise  ;  many  of  the  minute  branches  of  some  of  these  extend  to  the 
walls  of  the  alimentary  canal  and  thus  tend  to  hold  it  in  place. 

In  connection  with  the  tracheae,  the  action  of  the  masses  of  adipose  tissue 
should  be  observed.  These  large  masses,  which  to  a  great  extent  are  held 
in  place  by  the  tracheae  that  extend  to  the  alimentary  canal,  serve  as  cushions 
which  tend  to  keep  the  organ  in  place. 

By  muscles. — A  large  number  of  very  delicate  muscles  extend  from  the 
ventral  wall  of  the  head  to  the  oesophagus.  In  the  specimen  which  the  stu- 
dent is  now  studying,  only  the  ends  of  these  muscles  which  are  attached  to 
the  oesophagus  can  be  observed,  as  the  attachments  of  these  muscles  to  the 
wall  of  the  head  were  cut  away  in  the  preparation  of  the  specimen.  Large 
muscles  extend  caudo-ventrad  to  the  intestine  from  the  line  on  the  dorsal  wall 
of  the  body  between  the  eighth  and  ninth  abdominal  segments.  From 
within  the  anal  prolegs,  muscles  extend  cephalad  into  the  ninth  abdominal 
segment  and  are  attached  to  the  intestine.  Other  muscles  are  described  in 
the  next  section. 

By  the  stispensoria  of  the  viscera. — There  are  several,  long,  fine  threads 
that  are  so  attached  as  to  tend  to  hold  the  alimentary  canal  and  other  viscera 
in  place.     These  may  be  termed  collectively  the  suspensoria  of  the  viscera. 


38 

In  Corydalis  four  pairs  of  suspensoria  can  be  distinguished.  There  are  two 
pairs  of  suspensory  muscles,  a  pair  of  ligaments,  and  a  pair  of  suspensory 
nerves. 

The  suspensory  muscles  arise  from  the  body-wall  in  the  thorax,  and  ex- 
tend caudad  into  the  abdomen,  where  both  pairs  are  attached  to  the  aliment- 
ary canal,  and  one  pair  to  other  viscera  also.  It  is  rather  difficult  to  trace 
out  the  origins  of  these  threads  upon  the  body-wall ;  but  the  threads  can  be 
easily  seen  extending  parallel  with  the  oesophagus  and  proventriculus,  after 
they  emerge  from  the  layer  of  muscles  and  fat.  They  can  be  rendered  more 
easily  seen  by  staining  the  specimen  with  haematoxylin.  Empty  the  water 
from  the  dish  containing  the  specimen,  and  place  a  few  drops  of  haematoxy- 
lin  on  it ;  after  one  or  two  minutes  wash  off  the  stain,  and  cover  the  speci- 
men with  clean  water. 

Study  first  the  suspensoria  on  one  side  of  the  specimen,  leaving  those  of 
the  other  side  for  study  when  the  final  drawing  is  made.  In  the  following 
notes  a  single  member  of  each  pair  of  suspensoria  is  described. 

The  two  suspensory  muscles  may  be  designated  as  the  simple  suspensory 
muscle  and  the  branched  suspensory  muscle,  respectively. 

The  simple  suspensory  muscle  arises  from  near  the  middle  of  the  ental 
surface  of  the  pronotum,  and  extends  caudad  to  the  gastric  caeca,  where  the 
fibers  of  which  it  is  composed  spread  apart,  some  going  to  one  caecum  and 
some  to  the  other. 

Make  a  provisional  sketch  of  this. 

With  fine-pointed  scissors,  cut  off  the  tips  of  the  two  gastric  caeca  of  this 
side,  and  remove  them  with  as  long  a  piece  of  the  suspensory  muscle  as  is 
practicable,  and  mount  them  in  glycerine  for  study  with  a  high  power  of  the 
microscope.  Note  the  transversely  striated  appearance  of  the  fibers  of  this 
suspensorium.     This  indicates  that  it  is  composed  of  striated  muscular  tissue. 

Make  a  careful  drawing  showing  the  minute  structure  of  this  suspen- 
sorium. 

The  branched  suspensory  vuiscle  arises  from  the  ental  surface  of  the  body- 
wall,  on  the  dorsal  side,  between  the  mesothoracic  and  metathoracic  shields, 
near  the  lateral  margin  of  the  body  and  extends  caudad  into  the  cavity  of 
the  abdomen  ;  here  it  divides  into  several  branches.  One  branch  extends 
to  the  ventriculus  ;  one  or  more  to  the  masses  of  fat  and  to  the  Malpighian 
vessels  ;  and  one  joins  a  suspensorium  which  extends  from  a  large  trachea 
in  the  third  abdominal  segment  to  the  intestine. 

Trace  out  the  course  of  the  branches  of  the  branched  suspensory  muscle, 
and  make  a  provisional  sketch  showing  their  connections. 


39 

The  ligament  of  the  viscera  is  not  attached  to  the  body-wall,  but  is  sup- 
ported by  a  large  trachea  in  the  third  abdominal  segment,  about  which  it- 
forms  a  collar.  This  suspensorium  has  three  branches  ;  one  of  these  ex- 
tends caudad  to  the  testis  or  ovary ;  one,  cephalad,  to  the  heart ;  and  the 
third,  to  the  intestine.  This  last  branch  receives  the  tendon  of  one  of  the 
branches  of  the  branched  suspensory  muscle. 

Make  a  drawing  representing  the  alimentary  canal  in  the  center,  a  testis  or 
ovary  on  each  side  (these  are  described  in  the  next  section),  and  the  three 
pairs  of  suspensoria.  While  doing  this  the  provisional  sketches  already 
made  can  be  utilized,  but  the  observations  should  be  confirmed  by  a  sfudy 
of  the  suspensoria  of  the  other  side  of  the  specimen. 

Cut  the  trachea  supporting  the  ligament  of  the  viscera,  and  slip  the  liga- 
ment off  from  it ;  cut  the  ligament  extending  to  the  heart  as  near  to  the 
heart  as  practicable ;  cut  the  ligament  extending  to  the  intestines  between 
the  intestine  and  the  tendon  of  the  branched  suspensory  muscle ;  cut  the 
branched  suspensory  muscle  as  far  cephalad  as  practicable  ;  cut  off  the  tip 
of  the  testis  or  ovary,  leaving  it  attached  to  the  ligament ;  mount  the  prepa- 
ration thus  made  in  glycerine  for  study  with  the  microscope,  carefully  spread- 
ing  apart  the  branches  of  the  ligament  and  the  end  of  the  suspensory  muscle 
with  a  needle  before  putting  on  the  cover-glass.  Study  this  preparation 
with  a  high  power  of  the  microscope  and  note  the  difference  in  structure 
between  the  suspensory  muscle  and  the  ligament  of  the  viscera.  Make  a 
drawing  showing  this. 

The  suspensory  nerves  of  the  alimentary  canal  extend  from  the  small  in- 
testine to  the  last  abdominal  ganglion.  They  can  be  best  seen  in  a  speci- 
men opened  on  the  back  and  will  be  described  later. 

The  masticatory  organs  of  the    proventriculus. — 

Remove  the  alimentary  canal,  and  carefully  open  the  proven- 
triculus by  a  longitudinal  slit.  Cover  a  piece  of  cork  with 
white  paper,  spread  out  the  opened  proventriculus  upon  the 
paper,  ental  side  uppermost,  and  fasten  it  in  place  with  rib- 
bon-pins. Fasten  the  cork  bearing  the  preparation  to  the 
beeswax  in  a  dissecting  dish,  and  cover  the  preparation 
with  water.  Study  it  with  a  lens  and  with  a  compound 
microscope,  using  a  low  power.  Write  a  description  of 
the  masticatory  organs,  and  make  a  drawing  illustrating 
them. 


40 

The  reproductive  organs. — Although  there  appears  ta 
be  no  external  characteristic  by  which  the  sexes  of  the  larva 
of  Corydalis  can  be  distinguished,  the  internal  reproductive 
organs  differ  greatly  in  appearance  ;  the  testes  in  this  species 
are  long  and  narrow,  while  the  ovaries  are  short  and  broad. 
These  organs  are  situated  one  on  each  side,  between  the 
layer  of  adipose  tissue  which  surrounds  the  alimentary  canal 
and  the  layer  of  the  same  tissue  which  is  attached  to  the 
sides  of  the  wall  of  the  abdomen.  The  testes  extend  from 
near  the  middle  of  the  third  abdominal  segment  to  near  the 
posterior  border  of  the  sixth  abdominal  segment.  The  ova- 
ries extend  from  near  the  middle  of  the  fourth  abdominal 
segment  to  near  the  middle  of  the  fifth  abdominal  segment. 

Determine  the  sex  of  the  specimen  that  you  are  studying. 

Reproductive  Organs  of  the  Male. — Note  the  shape  of  a  testis,  the  con- 
nection of  it  with  the  respiratory  system,  the  groove  in  the  middle  of  its 
mesal  aspect,  and  the  vessel  in  the  bottom  of  this  groove.  This  vessel  is  the 
seminal  duct  or  vas  deferens  (plural,  vasa  deferentia)  and  is  the  outlet  of 
the  testis  ;  it  extends  caudad  to  near  the  caudal  end  of  the  body.  The 
cephalic  end  of  the  testis  is  supported  by  the  ligament  of  the  viscera  already 
described. 

Make  drawings  showing  the  external  form  of  a  testis. 

Trace  out  the  course  of  the  vas  deferens.  This  will  require  very  careful 
dissection,  especially  in  the  ninth  abdominal  segment,  where  the  vas  defer- 
ens passes  under  a  muscle. 

The  triangular  organ  into  which  the  two  vasa  deferentia  empty  is  the 
seminal  vesicle.  If  the  specimen  has  been  opened  on  the  ventral  side,  the 
seminal  vesicle  will  lie  on  the  alimentary  canal,  but  if  it  has  been  opened  on 
the  dorsal  side  it  will  be  necessary  to  cut  the  intestine  and  turn  back  the 
caudal  part  of  it  in  order  to  see  the  seminal  vesicle. 

The  tube  extending  from  the  seminal  vesicle  to  the  external  opening  of 
the  reproductive  organs  is  the  ejaculatory  duct. 

Make  a  drawing  showing  the  relations  of  the  testes,  vasa  deferentia,  semi- 
nal vesicle,  and  ejaculatory  duct. 

Each  testis  is  composed  of  many,  short,  pear-shaped  tubes,  the  testicular 
follicles,  in  which  the  spermatozoa  are  developed.     These  tubes  open  into 


41 

the  vas  deferens,  which,  as  alrea'dy  described,  extends  along  the  groove  in 
the  testis.  The  testicular  follicles,  however,  are  enclosed  in  a  thick  coat  of 
connective  tissue  which  conceals  them. 

Reproductive  Organs  of  the  Female. — Note  the  shape  of  an  ovary,  the 
connection  of  it  with  the  respiratory  system,  the  position  of  the  oviduct 
(which  is  the  vessel  extending  caudad  from  the  ovary),  and  the  attachment 
of  the  ligament  of  the  viscera. 

Make  a  drawing  showing  these  things. 

Each  oviduct  extends  caudad  from  the  caudal  end  of  the  ovary  through 
masses  of  fat  to  the  seventh  abdominal  segment,  where,  at  a  point  opposite 
the  last  ganglion  of  the  nervous  system,  it  passes  under  the  ventral  muscles, 
and  terminates  in  a  disc-like  enlargement,  on  the  body-wall. 

Make  a  dissection  showing  this. 

Note. — In  the  adult  the  two  oviducts  extend  caudad  to  near  the  caudal 
end  of  the  body  where  they  empty  into  a  short  vagina. 

Each  ovary  is  composed  of  many  parallel  tubes,  the  egg-tubes,  in  which 
the  eggs  are  developed,  and  which  open  into  the  oviduct.  But  as  the 
egg-tubes  are  enclosed  in  a  thick  coat  of  connective  tissue,  which  en- 
velopes the  entire  ovary,  it  is  necessary  to  break  this  coat  in  order  to  see 
them. 

Remove  an  ovary,  place  it  on  a  glass  slip,  tease  it  apart  with  needles,  and 
examine  it  with  a  microscope. 

Make  a  drawing  of  an  egg-tube. 

The  reproductive  organs  of  a  locust. — As  the  repro- 
ductive organs  of  the  larva  of  Corydalis  are  in  an  immature 
condition,  it  will  be  well  for  the  student  to  study,  at  this 
point  in  his  work,  the  reproductive  organs  of  an  adult  insect. 
For  this  purpose  the  red-legged  locust  may  be  used.  If  pos- 
sible use  fresh  specimens. 

The  reproductive  organs  of  the  male. — Remove  the  wings 
and  legs  from  an  adult  male  locust,  make  a  slit  in  the  dorsal 
wall  of  the  body,  extending  the  whole  length  of  the  thorax 
and  abdomen,  spread  open  the  specimen,  pin  it  to  a  piece  of 
cork,  and  place  it  under  water  for  dissection. 

The  testes  lie  upon  the  stomach,  and  are  enclosed  in  a  com- 
mon sack-like  envelope.     This  is  exceptional  ;   in  most  in- 


42 

sects  the  two  testes  are  separate,  each  lying  in  one  side  of 
the  body-cavity. 

The  cephalic  end  of  the  united  testes  is  supported  by  the 
ligament  of  the  viscera,  which  is  a  very  slender  cord,  extend- 
ing to  the  dorsal  wall  of  the  body. 

Break  the  envelope  enclosing  the  testes  and  note  that  they 
are  composed  of  many,  long,  slender  tubes  ;  these  are  the 
testicular  follicles. 

Separate  the  two  sets  of  follicles  and  observe  that  those  of 
each  side  empty  into  a  slender  duct ;  this  is  the  vas  deferens. 
The  two  vasa  deferentia  pass  caudo-ventrad,  one  on  each 
side  of  the  alimentary  canal. 

Cut  in  two  the  alimentary  canal  between  the  testes  and 
remove  the  caudal  portion  of  it. 

Observe  the  two  bundles  of  tubes  which  occupy  a  consid- 
erable part  of  the  cavity  of  the  abdomen  ;  these  are  the  semi- 
nal vesicles  and  the  accessory  glands.  There  is  on  each  side  a 
single,  long,  much  convoluted,  accessory  gland,  and  a  bundle 
of  shorter,  tubular  seminal  vesicles.  The  seminal  vesicles  are 
reservoirs  for  the  products  of  the  reproductive  organs  ;  the 
function  of  the  accessory  glands  has  not  been  determined, 
they  may  secrete  the  more  fluid  part  of  the  semen. 

Trace  out  the  course  of  the  vasa  deferentia,  and  note  that 
each  is  joined  by  the  seminal  vesicles,  and  the  accessory 
gland  of  the  same  side,  and  that  almost  immediately  the  tubes 
of  the  two  sides  unite,  forming  a  single  tube  ;  this  is  the 
ejaculatory  duct. 

The  ejaculatory  duct  leads  to  the  penis  j  owing  to  the 
muscles  surrounding  this  organ  the  determination  of  its  form 
is  quite  difficult,  and  will  be  omitted  in  this  elementary  course. 

If  fresh  specimens  are  available,  kill  one  in  a  cyanide  bot- 
tle, and  by  pressure  of  the  abdomen  force  out  the  caudal  end 
of  this  organ,  and  observe  the  chitinous  hooks  with  which  it 
is  armed. 


43 

Dissect  another  specimen,  opening  it  on  the  ventral  side. 

Make  a  diagram  representing  the  relations  of  the  various 
parts  of  the  reproductive  organs  of  the  male  locust. 

If  fresh  specimens  can  be  obtained,  kill  one,  remove  a 
seminal  vesicle  from  it,  tease  apart  the  vesicle  on  a  glass 
slip,  mount  it  in  glycerine,  examine  it  with  a  high  objective, 
and  observe  the  bundles  of  spermatozoa.  Each  bundle  con- 
sists of  a  great  number  of  hair-like  spermatozoa. 

The  reproductive  organs  of  the  female.  —  Take  an  adult 
female  locust,  remove  the  wings  and  hind  legs,  and  make  a 
slit  in  the  dorsal  wall  of  the  body  extending  the  whole  length 
of  the  thorax  and  abdomen.  Spread  open  the  specimen,  pin 
it  to  a  piece  of  cork,  and  place  it  under  water  for  dissection. 

The  ovaries  lie  above  and  on  each  side  of  the  stomach  : 
the  cephalic  end  of  them  is  supported  by  the  ligament  of  the 
viscera.  The  egg-tubes  of  which  the  ovaries  are  composed 
occupy  the  same  relative  position  as  the  testicular  follicles  of 
the  male,  but  fill  a  larger  proportion  of  the  body-cavity. 

Push  laterad  the  egg-tubes  of  each  side  so  as  to  expose 
the  alimentary  canal  ;  cut  in  two  the  alimentary  canal  in  the 
thorax,  and  remove  the  caudal  portion  of  it  ;  this  will  expose 
two  large  bundles  of  muscles  connected  with  the  dorsal  pair 
of  valves  of  the  ovipositor.  Carefully  split  these  apart  and 
fasten  them  aside  with  pins.  When  this  is  done,  the  last 
ganglion  of  the  nervous  system  will  be  exposed.  Carefully 
remove  this  ganglion,  cutting  such  nerves  and  tracheae  as 
may  be  necessary. 

Each  ovary  consists  of  many  egg-tubes  which  are  arranged 
in  two  rows,  and  open  into  an  mndnct ;  the  two  oviducts  unite 
near  the  caudal  end  of  the  body  and  form  the  common  ovi- 
duct or  vagina. 

That  portion  of  each  oviduct  into  which  the  egg-tubes 
empty  is  greatly  enlarged  ;  this  is  termed  the  egg-calyx,  and 
serves  as  a  receptacle  for  the  ripe  eggs. 


44 

There  is  a  prolongation  of  each  oviduct  which  extends 
cephalad  of  the  ovar}'  ;  this,  we  infer  is  a  coUeterial  gland. 
The  colleterial  glands  are  organs  which  secrete  the  cement 
for  gluing  together  the  eggs  ;  the  more  usual  form  of  them 
is  that  of  separate  glands,  like  the  accessory  glands  of  the 
male,  which  open  into  the  vagina,  as  the  accessory  glands 
open  into  the  ejaculatory  duct. 

Lying  dorsad  of  the  vagina,  there  is  a  small  elongate  body, 
from  which  there  extends  a  much  convoluted  tube  ;  these 
are  the  spermatheca  and  its  duct. 

On  each  side  of  the  vagina,  near  the  caudal  end  of  the 
body  there  is  a  rounded  pouch,  which  in  fresh  specimens  is 
of  a  reddish  color.  From  the  cephalic  end  of  each  pouch  a 
muscle  passes  cephalad  along  the  dorsal  wall  of  the  vagina, 
and  between  the  two  oviducts,  and  is  attached  to  the  ventral 
wall  of  the  body.  These  pouches  open  below  the  ventral 
valves  of  the  ovipositor,  one  on  each  side  of  the  opening  of 
the  vagina,  but  a  .little  farther  dorsad  than  that  opening. 
The  function  of  these  organs  has  not  been  determined  ; 
they  are  described  here  on  account  of  their  intimate  rela- 
tions with  the  reproductive  organs.  They  are  doubtless 
eversible  glands,  as  in  fresh  specimens  they  can  be  everted 
by  pressure  ;  and  the  muscles  are  doubtless  for  withdrawing 
them  after  eversion. 

If  living  specimens  are  available,  kill  a  female,  by  putting 
it  in  a  cyanide  bottle,  and  then  by  pressure  of  the  abdomen 
evert  these  glands.  Note  that  they  open  separately  between 
the  last  sternum  of  the  abdomen  and  the  ventral  valves  of 
the  ovipositor. 

Take  a  fresh  specimen,  or  a  preserved  one,  if  fresh  speci- 
mens are  not  to  be  had,  and  spread  apart  the  last  sternum 
of  the  abdomen  and  the  ovipositor,  and  observe  the  elliptical 
opening  between  the  ventral  valves  of  the  ovipositor.  This 
opening  is   surrounded   by  narrow  bands  of    chitin,  and    is 


45 

the  opening  of  the  bursa  copulatrix.  It  is  through  this  opening 
that  the  seminal  fluid  is  received. 

The  opening  of  the  vagina  is  distinct  from  that  of  the  bursa 
copulatrix,  and  ventrad  of  it.  It  is  on  the  dorsal  aspect 
of  the  lobe  of  the  body  supported  by  the  last  abdominal 
sternum. 

Return  now  to  the  study  of  your  dissection. 

Trace  out  the  course  of  the  duct  leading  from  the  sperma- 
theca  and  observe  that  it  empties  into  a  pouch  ;  this  is  the 
bursa  copulatrix,  the  external  opening  of  which  has  been  ex- 
amined already. 

Trace  out  the  course  of  the  vagina  and  observe  that  its 
opening  is  distinct  from  that  of  the  bursa  copulatrix,  as  has 
been  pointed  out. 

When  the  eggs  are  laid  they  are  pushed  dorsad  past  the 
opening  of  the  bursa  copulatrix,  in  this  way  spermatozoa 
coming  from  the  spermatheca  can  reach  them.  The  egg- 
shell of  insects  is  perforated  at  one  end  by  one  or  more 
openings,  the  micropyle  through  which  a  spermatozoon  passes 
to  fertilize  the  egg. 

Dissect  another  specimen,  opening  it  on  the  ventral  side. 

Make  a  diagram  representing  the  relations  of  the  parts  of 
the  reproductive  organs  of  a  female  locust. 

Review. — The  following  tabular  statement  will  aid  the 
student  in  making  a  review  of  his  work  oh  the  reproductive 
organs  of  a  locust,  and  will  serve  to  indicate  the  correspond- 
ence of  the  parts  in  the  two  sexes.  He  should  bear  in  mind, 
however,  that  the  reproductive  organs  of  different  insects 
vary  greatly  in  structure.  In  most  insects  each  testis  or 
ovary  consists  of  many  parallel  tubes,  as  in  the  locust ;  but 
the  structure  and  position  of  the  reservoirs  of  the  products 
of  these  organs  and  the  structure  of  the  accessory  glands 
differ  greatly  in  different  insects. 


46 


REPRODUCTIVE    ORGANS    OF    A    LOCUST. 


Two  testes,  each  testis  consisting 
of  many  testicular  follicles. 

Two  -c'asa  deferentia. 

Several  seminal  vesicles,  each 
an  appendage  of  a  vas  def- 
erens. 

Two  accessory  glands,  each  an 
appendage  of  a  vas  def- 
erens. 

An  ejaculatory  duct,  the  united 
vasa  deferentia. 

A  penis. 


II.       FEMALE. 

1.  Two  ovaries,  each  ovary  consist 
ing  of  many  egg-tiibes. 

2.  Two  oviducts. 

3.  Two  egg-calyces,  each  calyx  an 
enlarged  portion  of  an  ovi- 
duct. 

4.  Two  colleterial  glands,  each  a 
cephalic  prolongation  of  an 
oviduct. 

5.  A  vagina,  the  united  oviducts. 

6.  An  ovipositor. 

7.  A  bursa  copulatrix  and  a  sper- 
inatheca    with  a  duct  connect- 

ing them. 

The  respiratory  system. — Return  to  the  study  of 
Corydalis.  Make  a  diagram  showing  the  arrangement  of 
the  larger  tracheae. 

The  walls  of  the  tracheae  are 
composed  of  three  layers,  which 
correspond  to  the  layers  of  the 
body-wall  ;  in  fact  the  tracheae 
are  invaginations  of  the  body- 
wall.  The  continuity  of  the 
membranes  of  the  tracheae  and 
body-wall  is  shown  diagrammat- 
ically  in  Figure  i.  It  should 
be  observed  that  it  is  the  inner 
layer  of  the  wall  of  the  tracheae 
that  corresponds  with  the  outer 
layer  of  the  wall  of  the  body. 

This  inner  layer  of  the  wall  of 
the   trachea,  the  intima,  like  the 
cuticle,  is  chitinous,  and  is  shed 
from  the  tracheae  with  the  cuticle  when    the    insect  molts. 
This  layer  of  the  trachea  is  furnished  with  thickenings,  which 


Fig.  I. — Section  of  trachea  and 
body-wall,  c,  cuticle  ;  hy,  hypo- 
dermis  ;  sp,  spiral  thickening  of 
the  intima.  The  third  layer  is 
a  delicate  membrane  bounding 
the  ental  ends  of  the  hypoder- 
mal  cells  ;  this  is  the  basement 
membrane. 


47 

extend  spirally  and  give  to  tracheae  their  characteristic, 
transversely  striated  appearance.  If  a  piece  of  one  of  the 
larger  tracheae  be  pulled  apart  the  intima  will  tear  between 
the  folds  of  the  spiral  thickening,  and  the  latter  will  uncoil 
from  within  the  trachea  like  a  thread.  These  spiral  thicken- 
ings are  termed  tanidia  (Greek,  little  bands).  In  some  insects 
there  are  several,  parallel  thickenings  of  the  intima,  so  that, 
when  an  attempt  is  made  to  uncoil  the  taenidia,  a  ribbon-like 
band  is  produced, which  is  composed  of  several  parallel  taenidia. 

Make  a  preparation  and  a  drawing  illustrating  the  appear- 
ance of  a  trachea  of  Corydalis,  with  the  tanidia  partially 
uncoiled. 

The  heart  and  the  aorta. — Read  the  account  of  the 
blood-vessels  in  Comstock's  Matiual  for  the  Study  of  Insects, 
pp.  71,  72. 

'In  Corydalis  the  dorsal  blood-vessel  extends  from  the 
eighth  abdominal  segment  to  the  brain.  It  is  a  slender  tube, 
widest  in  the  region  of  the  fourth  and  fifth  abdominal  seg- 
ments. That  part  of  it  which  lies  in  the  abdomen  is  the 
heart ;  the  more  slender  portion  which  traverses  the  thorax 
and  extends  into  the  head  is  the  aorta. 

The  cephalic  end  of  the  aorta  is  attached  to  the  brain,  and 
is  trumpet-shaped  except  that  the  ventral  wall  of  it  is  split. 
In  this  way  a  V-shaped  opening  is  formed,  through  which 
the  blood  flows  out,  into  the  cavity  of  the  head. 

Make  a  drawing  representing  the  outline  of  the  heart  and 
the  aorta. 

The  valves  of  the  heart  and  of  the  aorta. — Usually  it  is  very  diffi- 
cult to  determine  the  position  and  form  of  the  valves  in  the  dorsal  blood- 
vessel in  specimens  preserved  in  chloral  hydrate  solution  ;  for  a  study  of 
these  valves  specimens  which  have  been  prepared  especially  for  this  pur- 
pose are  necessary.  On  this  account  this  part  of  the  subject  may  be  omit- 
ted by  students  taking  a  brief  course  in  entomology.  For  the  sake  of 
others  the  following  method  of  study  is  indicated : 


48 

With  a  hypodermic  syringe  inject  into  the  body-cavity  of  a  living  larva  a 
solution  of  lampblack  or  of  carmine.*  After  about  an  hour,  drop  the  larva 
into  boiling  water  and  leave  it  there  till  killed,  which  will  require  from  ten 
to  twenty  seconds  ;  then  transfer  it  to  cold  water.  In  specimens  prepared 
in  this  way  the  heart  will  be  found  fi-lled  with  coagulated. blood,  which  is 
rendered  more  easily  seen  by  the  presence  in  it  of  the  lampblack  or  carmine. 
The  relation  of  the  valves  to  the  segments  of  the  body  can  be  best  deter- 
mined in  specimens  from  which  the  dorsal  body-wall  has  been  removed 
from  over  the  heart,  the  specimens  being  studied  from  the  dorsal  aspect. 

In  Corydalis  the  heart  contains  eight  sets  of  valves,  and  the  aorta  two. 

Make  figures  showing  the  position  and  form  of  the  valves  of  the  heart 
and  of  the  aorta. 

The  pericardial  diaphragm  or  the  "  wings  of  the 
heart." — Take  the  specimen  which  was  prepared  so  as  to 
show  the  heart  and  the  aorta.  Empty  the  water  from  the 
dish  containing  the  specimen,  and  place  a  few  drops  of 
haematoxylin  on  it  ;  after  one  or  two  minutes  wash  off  the 
stain,  and  cover  the  specimen  with  clear  water.  Careful 
examination  will  now  reveal  the  dorsal  diaphragm,  which  is 
so  delicate  that  it  is  seen  with  difficulty  unless  stained. 

This  diaphragm  is  attached  along  its  middle  line  to  the 
ventral  surface  of  the  heart.  Each  lateral  edge  of  the 
diaphragm  is  attached  to  the  body-wall  in  sixteen  places^ 
along  two  lines. 

Represent  the  pericardial  diaphragm  upon  the  drawing  of 
the  heart  and  aorta  already  prepared. 

There  are  differences  of  opinion  as  to  the  function  of  the 
pericardial  diaphragm. f  It  seems  to  us  that  an  important 
function,  if  not  its  chief  function,  is  to  protect  the  heart 
from  the  peristaltic  movements  of  the  alimentary  canal.  It 
also  supports  the  heart ;  and  may  play  a  part  in  its  expan- 
sion. 

*.2  g.  lampblack,  .2  g.  gum  arable,  15  c.  c.  water;  or  .4  g.  carmine,  .2  g. 
gum  arable,  15  c.  c.  water. 

t  See  Packard.     Text  Book  of  Entomology,  pp.  401,  402. 


49 

Review. — Take  a  specimen  that  has  been  slit  on  the 
dorsal  surface  and  make  a  preparation  similar  to  the  one  just 
studied  except  that  it  is  opened  on  the  back.  Review  the 
work  on  internal  anatomy  indicated  above  excepting  those 
parts  referring  to  the  nervous  system,  which  will  be  con- 
cealed by  the  alimentary  canal  in  this  specimen,  and  to  the 
circulatory  system,  which  will  be  destroyed  in  the  prepara- 
tion of  the  specimen. 

Note  especially  the  form  of  the  reproductive  organs  and 
determine  if  the  specimen  is  of  the  same  sex  as  the  one  pre- 
viously studied.  If  it  is  not,  complete  the  work  on  the  re- 
productive organs  indicated  above  ;  if  it  is  of  the  same  sex, 
other  specimens  should  be  examined  after  the  work  on  this 
one  is  completed. 

The  suspensory  nerves  of  the  alimentary  canal. — Gently  push 
the  intestine  to  one  side  and  note  the  two  fine  threads  extending  caudad 
from  the  small  intestine.  Trace  out  the  connection  of  these  threads  or 
nerves  with  the  nervous  system.  Note  the  fine  branches  of  these  nerves 
that  extend  to  the  caudal  part  of  the  intestine. 

Make  a  diagram  representing  a  side  view  of  that  part  of  the  alimentary 
canal  caudad  of  the  proventriculus,  the  last  three  ganglia  of  the  nervous 
system,  and  the  nerves  just  described. 

The  ventral  diaphragm. — Cut  the  alimentary  canal  in 
two  between  the  ventriculus  and  the  first  bend  in  the  intes- 
tine. Remove  that  part  of  the  alimentary  canal  caudad  of 
this  point.  Cut  the  tracheae  of  one  side  extending  to  the 
remaining  part  of  the  alimentary  canal,  so  that  it  can  be 
pushed  away  to  the  other  side.  Be  careful  not  to  injure  this 
part  of  the  alimentary  canal  till  after  the  vagus  nerve  has 
been  studied,  as  indicated  in  a  later  paragraph.  Empty  the 
water  from  the  dish  containing  the  specimen  and  put  a  few 
drops  of  hsematoxylin  solution  on  the  muscles  and  nerves  in 
the  abdomen  ;  after  one  or  two  minutes,  wash  off  the  stain, 
and  cover  the  specimen  with  clear  water  ;  observe  the  ven- 


50 

tral  diaphragm.  This  is  a  transparent,  apparently  structure- 
less membrane,  stretched  over  the  floor  of  the  abdominal 
cavity  in  such  a  way  as  to  protect  the  central  part  of  the 
nervous  system.  Owing  to  the  transparency  of  this  mem- 
brane, it  is  very  difficult  to  see  it  unless  it  is  stained.  The 
ventral  diaphragm  is  attached  along  each  side  of  the  body 
just  laterad  of  the  great  ventral  muscles  ;  the  points  of  at- 
tachment are  on  the  lines  separating  the  segments  of  the 
body.  Between  the  points  of  attachment,  the  margins  of 
the  membrane  curve  mesad,  giving  it  the  appearance  of  be- 
ing strongly  stretched  at  the  points  of  attachment. 

This  diaphragm  has  been  described  as  a  ventral  heart. 
See  Packard,  Text  Book  of  Entomology,  p.  403.  We  believe  its 
function  is  to  protect  the  central  nervous  system  from  the 
peristaltic  movements  of  the  alimentary  canal. 

The  nervous  system. — After  removing  the  alimentary 
canal  from  the  specimen  opened  along  the  back,  the  central 
nervous  system  will  be  exposed. 

Make  a  diagram  showing  the  disposition  of  the  ganglia 
and  of  the  principal  nerves  of  the  thorax  and  abdomen. 
These  can  be  seen  better  in  a  specimen  which  has  been 
opened  along  the  venter.  Take  for  this  purpose  either  a 
fresh  specimen  or  one  that  has  been  slit  on  the  dorsal  side, 
and  open  it  carefully  on  the  ventral  side  so  as  to  cut  through 
only  the  body-wall,  leaving  the  nervous  system  in  place. 

Make  careful  dissections  of  the  ganglia  and  nerves  found 
in  the  head,  and  make  a  diagram  showing  their  arrangement. 

The  following  parts  should  be  observed  and  figured  : — 

The  supraoesophageal  ganglia. — These  are  two,  large,  ovoid 
ganglia,  lying  above  the  oesophagus,  and  connected  by  a 
short,  thick  commissure.  They  are  sometimes  termed  the 
brain. 

The  antennal  nerves. — These  arise  from  the  latero-cephalic 
angles  of  the  supraoesophageal  ganglia. 


51 

The  optic  nerves. — These  arise  caudad  of  the  origins  of 
the  antennal  nerves.  Determine  the  number  of  divisions  of 
each  optic  nerve. 

The  crura  cerebri. — These  are  the  two,  large  cords,  one  on 
each  side,  connecting  the  supraoesophageal  ganglia  with  the 
suboesophageal  ganglion,  and  forming  with  these  ganglia  the 
nervous  collar  of  the  oesophagus.  (The  singular  form  of 
crura  is  crus.) 

The  vagus  nerve. — Just  cephalad  of  the  supraoesophageal 
ganglia  there  is  a  minute  ganglion,  the  frontal  ganglion ; 
this  is  connected  by  an  arching  nerve  on  each  side  with  the 
crura  cerebri  ;  from  the  frontal  ganglion  there  extends  ceph- 
alad a  small,  branching  nerve  ;  from  the  frontal  ganglion 
there  also  extend  two  nerves  which  pass  caudad  ;  one  of 
these  extends  to  the  commissure  connecting  the  supra- 
oesophageal ganglia;  the  other  passes  between  the  supra- 
oesophageal ganglia  and  the  oesophagus,  and  ventrad  of  the 
aorta  (which  is  usually  turned  to  one  side  in  opening  the 
specimen  as  this  one  is  opened),  to  a  minute  ganglion  on  the 
middle  line  of  the  oesophagus,  caudad  of  the  supraoesopha- 
geal ganglia.  From  this  minute  ganglion  two  nerves  extend, 
one  on  each  side,  to  the  sides  of  the  alimentary  canal,  which 
they  follow  to  the  proventriculus,  where  they  divide  into 
many  branches.  This  system  of  nerves  and  ganglia  is 
termed  the  vagus  nerve. 

The  suboesophageal  ganglion. — This  is  the  large  ganglion  on 
the  meson,  ventrad  of  the  oesophagus.  From  it  two  large 
cords  pass  caudad  to  the  first  thoracic  ganglia. 

From  the  suboesophageal  ganglia  nerves  extend  to  the  labi- 
um, the  maxillae,  the  mandibles,  and  to  other  parts  of  the  head. 
The  beginning  students  who  are  taking  a  short  course  in  ento- 
mology need  not  trace  out  these  nerves.  Other  students  may 
use  as  a  work  of  reference  a  paper  on  this  subject  by  Dr. 
William  C.  Krauss,  published  in  "Z'^^y^y^^,"  vol.  IV.,  pp.  179-184. 


52 

The  muscular  system. — In  a  fresh  specimen  the  mus- 
cles appear  soft  and  translucent ;  but  in  specimens  that  have 
been  kept  for  a  considerable  time  in  a  preservative  fluid, 
they  are  firm  and  opaque.  The  greater  number  of  the  mus- 
cles are  attached  to  the  ental  surface  of  the  body-wall  where 
they  form  several  layers.  This  is  well  shown  in  the  abdo- 
men, where  most  of  the  muscles  are  for  moving  the  seg- 
ments of  the  body.  In  the  head  and  thorax,  there  are 
numerous  muscles  for  moving  the  appendages  of  the  body, 
and  their  arrangement  is  much  more  complicated. 

To  attempt  to  make  a  detailed  study  of  the  muscular  sys- 
tem would  require  much  more  time  than  can  be  devoted  to 
this  system  in  this  elementary  course.  Only  the  more  gen- 
eral features  of  the  structure  of  the  muscles  and  of  their 
arrangement  will  be  noticed. 

Note  that  the  muscular  system  is  composed  of  an  im- 
mense number  of  distinct,  isolated,  straight  fibers,  which  are 
not  enclosed  in  tendinous  sheaths  as  they  are  with  verte- 
brates. 

Mount  a  few  of  these  fibers  in  glycerine,  and  study  them 
with  a  high  power  of  the  microscope.  Note  that  the  fibers 
present  numerous,  transverse  striations,  like  the  striped  mus- 
cles of  vertebrates. 

Make  a  figure  of  a  muscular  fiber. 

In  this  outline  each  series  or  layer  of  closely  parallel 
fibers  is  considered  as  a  separate  muscle  rather  than  an 
aggregation  of  muscles.  It  complicates  the  subject  unduly 
to  consider  each  distinct  fiber  a  distinct  muscle  as  has  been 
done  by  some  writers.  Thus  Lyonet  in  his  "  Traite  Ana- 
tomique  de  la  Chenille,  que  range  le  bois  de  saule  "  describes 
1,647  muscles  without  including  the  muscles  contained  in  the 
viscera  or  those  contained  in  the  head. 

Take  a  larva  of  Corydalis,  which  has  been  opened  on  the 
ventral  side  and  from  which  the  alimentary  canal  and  the 


53 

larger  masses  of  fat  have  been  removed,  and  study  the  ental 
layer  of  muscles  of  the  dorsal  wall  of  the  abdomen. 

On  each  side  of  the  heart  and  ectad  of  the  wings  of  the 
heart,  there  are  great  bands  of  longitudinal  muscles,  occupy- 
ing the  space  between  the  heart  and  the  prominent  muscles 
that  extend  dorso-ventrad  on  the  sides  of  the  body.  Of  the 
longitudinal,  dorsal  muscles  there  are  two  sets  on  each  side. 
The  wider  set,  which  lies  near  the  heart,  may  be  termed  the 
great-dorsal-recti-muscles ;  the  narrower  set,  which  lies  be- 
tween the  great-dorsal-recti-muscles  and  the  dorso-ventral 
muscles  of  the  sides  of  the  body,  may  be  termed  the  small- 
dorsal-  recti-  muscles. 

Of  the  dorso-ventral  muscles  of  the  sides  of  the  body,  re- 
ferred to  above,  there  are  two  large  bundles  on  each  side  of 
each  segment  they  are  situated  near  the  union  of  the  seg- 
ments. 

Between  the  lateral  muscles  and  the  cut  edge  of  the  speci- 
men (the  dorsimeson)  lie  the  great -ventral -recti -muscles. 
These  differ  from  the  great-dorsal-recti-muscles  in  being 
somewhat  oblique  (this  is  shown  better  in  specimens  opened 
on  the  back). 

Make  a  drawing  of  the  third,  fourth,  and  fifth  abdominal 
segments  representing  the  muscles  mentioned  above. 

CarefuUy  remove  the  recti  muscles  in  one  or  two  abdomi- 
nal segments  and  note  that  ectad  of  them  are  many  muscles 
extending  obliquely  in  various  directions.  The  study  of 
these  oblique  muscles  will  be  omitted  in  this  course. 


CHAPTER  IV. 

ANATOMY    OF    THE    LARVA    OF    THE    GIANT    CRANE-FLY 
(HOLORUSIA   RUBIGINOSA). 

As  the  larvae  of  Corydalis  are  not  to  be  found  on  the 
Pacific  Coast  (and  in  some  other  parts  of  the  United  States) 
an  account  of  the  anatomy  of  the  larva  of  a  crane-fly  (Tipu- 
lids)  is  presented  for  the  use  of  students  who  may  not  be 
able  to  work  with  Corydalis.  The  largest  Tipulid  is  the 
Giant  Crane-fly,  Holorusia  rubiginosa,  found  commonly  on 
the  Pacific  Coast.  The  larvae  of  this  Tipulid  attain  a  length 
of  two  to  two  and  one-half  inches,  and  by  the  absence  of  fat 
in  the  body-cavity,  and  the  ease  with  which  they  may  be 
perfectly  preserved  and  readily  dissected  offer  especially 
available- subjects  for  the  study  of  the  internal  insect  anat- 
omy. As  Holorusia  does  not  occur  elsewhere  in  the  United 
States  than  on  the  Pacific  Coast  (as  far  as  is  known)  students 
in  other  regions  (in  which  Corydalis  also  does  not  occur)  will 
have  to  use  the  larva  of  some  other  Tipulid  species.  Some 
rather  large  Tipulid  is  common  in  almost  every  locality. 
The  account  of  Holorusia  will  be  found  to  answer  as  a  guide 
to  the  dissection  of  any  other  Tipulid  larva. 

EXTERNAL    ANATOMY. 

Technical  note. — Bring  a  number  of  the  larvae  of  Holo- 
rusia (or  other  large  Tipulid  species,  to  be  found  in  wet 
moss,  vegetable  slime  or  about  grass  roots  in  pastures,  etc.) 
alive  into  the  laboratory.     Note  the  various  motions  and  the 

54 


55 

locomotion  of  the  body.  Kill  specimens  by  dropping  into 
boiling  water.  After  the  specimens  have  straightened  out 
and  stiffened,  requiring  about  a  minute  (death  is  almost  in- 
stantaneous) remove  to  thirty  per  cent,  alcohol.  After  two 
or  three  hours  remove  to  fifty  per  cent,  alcohol,  and  after 
three  hours  into  seventy  per  cent,  alcohol.  After  twelve  to 
twenty-four  hours  remove  the  specimens  to  eighty-five  per 
cent,  alcohol,  in  which  keep  them. 

Structure  of  body. — (Verify  the  following  statements  if 
Holonisia  is  used  :  if  another  Tipulid  is  used  compare  con- 
ditions with  those  here  described.)  The  body  is  composed 
of  thirteen  segments  (exclusive  of  the  head).  Retracted  into 
the  (apparently)  first  and  second  segments  is  the  head,  with 
strongly  chitinized  skull.  At  the  anterior  end  of  the  head, 
usually  projecting  slightly,  are  the  short,  cylindrical,  unseg- 
mented  antenna  and  the  strongly  chitinized  mouth-parts. 
(The  mouth-parts  can  be  better  examined  after  the  larva 
has  been  dissected  and  the  retracted  head  wholly  exposed.) 

There  are  no  legs  or  tracheal  gills  (as  there  are  in  the  larva 
of  Corydalis).  The  hindmost  body-segment  bears  terminally 
on  a  flat  surface  two  large  spiracles  (breathing  openings,  see 
p.  74,  Comstock's  Manual),  surrounded  by  six  backward  pro- 
jecting flexible  lobes.  On  the  ventral  surface  of  this  seg- 
ment is  the  anal  opening  of  the  alimentary  canal  on  an  eleva- 
tion bearing  four  large  and  tv/o  smaller  flexible  processes. 
The  segments  of  the  hinder  half  of  the  body  have  each  a 
median  transverse  constriction  ;  those  of  the  anterior  half 
are  difficult  to  distinguish  from  one  another  but  it  is  as- 
sumed that  each  pair  of  the  lateral  groups  of  seta  of  which 
five  pairs  may  be  noted,  represents  a  segment.  The  ab- 
sence of  all  paired  appendages  back  of  the  head  is  to  be 
noted. 

Make  a  drawing  of  the  whole  oody  of  the  larva  from  a  lat- 
eral aspect. 


56 


INTERNAL    ANATOMY. 

Technical  note. — With  fine  scissors  cut  open  the  body 
along  the  median  line  of  the  dorsum,  cutting  through  only 
the  body-wall.  Put  the  specimen  in  a  dissecting  *  dish,  pin 
out  the  cut  edges  with  ribbon  pins  and  cover  with  water. 

Adipose  tissue. — The  most  conspicuous  organ  in  the 
opened  body-cavity  is  the  alimentary  canal  extending  as  a 
long  thick  tube  longitudinally  from  head  to  caudal  extremity. 
It  is  nearly  entirely  enclosed  in  a  thin,  whitish,  perforated 
sheet  of  adipose  tissue,  or  fat.  Note  the  disposition  of  this 
sheet.  Examine  a  small  piece  in  water  on  a  slide  under  the 
microscope,  first  under  low  power  and  then  under  higher 
power.  Make  a  drawing  showing  the  structure  of  adipose 
tissue  as  thus  shown. 

Alimentary  canal  and  accessory  parts. — The  aliment- 
ary canal  is  composed  of  a  series  of  successive  regions  or 
parts  ;  first  (foremost)  the  slender  oesophagus,  embraced  by 
the  circumoesophageal  ne?-ve  commissures  with  the  small  white 
brain  lobes  above  ;  second,  an  abruptly  dilated  conical  part, 
the  proi>entriculus  J  third,  a  part  immediately  behind  this  and 
not  sharply  marked  off  from  it,  the  elongated  vetitriculus 
bearing  at  its  anterior  end  four  elongated  pouches,  the  gas- 
tric cceca.  In  the  sheet  of  adipose  tissue  surrounding  the 
ventriculus  several  slender  convoluted  thread-like  processes 
may  be  seen  ;  these  are  the  Malpighian  tubules,  the  organs  of 
excretion,  four  in  number.  They  arise  from  the  alimentary 
canal  just  back  of  the  ventriculus  at  a  part  marked  by  a  pale 
transverse  line.  Behind  this  line  is  a  fourth  part  of  the  ali- 
mentary canal,  the  small  intestine.  It  is  of  smaller  caliber 
than  the  ventriculus  and  opens  into  a  succeeding  part  of  the 
canal,  the  large  intestine,  near  its  anterior  end.     The  large  in- 

•  For  directions  for  making  dissecting  dish  see  pp.  34-35. 


57 

testine  is  largest  in  front  and  tapers  posteriorly  to  the  very 
narrow  hinder  part  which  is  called  the  rectum.  That  portion 
of  the  large  intestine  in  front  of  the  point  of  entrance  of  the 
small  intestine  may  be  called  the  intestinal  ccecivn. 

For  an  account  of  the  functions  of  the  different  parts  of 
the  alimentary  canal  see  the  Cambridge  Natural  History, 
Vol.  v.,  pp.  123-127. 

Salivary  glands. — The  salivary  glands  lie  one  on  each 
side  of  the  oesophagus.  Each  is  a  white,  firm  U-shaped  body, 
with  the  two  arms  much  thickened,  and  the  inner  reaching 
a  little  farther  forward  than  the  outer.  The  salivary  duct 
arises  from  the  outer  lobe  ;  the  two  ducts  run  forward  and 
unite  beneath  the  oesophagus,  the  common  duct  thus  formed 
opening  into  the  mouth-cavity. 

Without  removing  the  alimentary  canal,  make  a  drawing 
of  it  and  the  salivary  glands  in  position  in  the  body. 

Examine  a  piece  of  salivary  duct  in  water  or  glycerine  on 
a  slide  under  the  microscope.  Note  the  transversely  striated 
condition.  Remove  the  cover-glass  and  with  needles  pull 
the  duct  gently  apart.  Examine  again  ;  the  two  parts  will 
probably  be  connected  by  a  spiral  thread ;  this  will  be 
seen  to  be  what  formed  the  transverse  striation  ;  it  is  really 
a  spiral  thickening  of  the  walls,  not  in  a  continuous  thread, 
but  in  a  series  of  short,  independent  spirals  of  one  or  few 
turns,  called  tc^nidia. 

The  respiratory  system. — The  external  openings,  spir- 
acles,  of  the  respiratory  organs,  have  already  been  noted  in 
the  examination  of  the  external  parts  of  the  specimen.  Each 
of  these  two  spiracles  opens  internally  into  a  main  air  tube, 
trachea,  which  runs  forward  through  the  whole  length  of  the 
body.  In  each  of  the  segments,  from  the  fourth  to  the  tenth 
inclusive  (not  counting  the  head),  a  large  branch  trachea  is 
given  off  from  the  main  longitudinal  trunk  to  the  alimentary 
canal,  and  a  smaller  one  to  the  dorsal  blood-vessel  (see  postea). 


58 

Make  a  drawing  of  the  tracheal  system,  tracing  the  longi- 
tudinal and  lateral  vessels  as  far  as  possible. 

Cut  off  a  small  piece  of  one  of  the  lateral  tracheae  and  ex- 
amine it  in  water  or  glycerine  on  a  slide  under  the  micro- 
scope. Note  the  tubular  character  of  the  trachea,  and  note 
the  five  transverse  striations  due  to  spiral  thickenings  of  the 
inner  wall  of  the  vessel.  Pull  apart  pieces  of  trachea  to  show 
the  tcenidia.  See  p.  47.  Make  a  drawing  of  a  piece  of 
trachea  to  show  its  structure. 

For  an  account  of  the  respiration  of  insects,  see  the  Cam- 
bridge Natural  History,  Vol.  V.,  pp.  128-132. 

The  reproductive  organs. — The  reproductive  organs 
consist  in  the  male  of  two  small,  white  oval  bodies,  the  testes, 
lying  one  on  each  side  of  the  large  intestine  imbedded  in  the 
muscles  of  the  tenth  body-segment,  and  of  a  delicate  duct, 
the  vas  deferens,  running  posteriorly  from  each  to  the  ventral 
wall  of  the  penultimate  segment.  In  female  specimens  the 
white  bodies,  ovaries,  are  larger  and  more  elongate  than  the 
testes  of  the  male,  and  the  otnducts  (corresponding  to  the  vasa 
deferentia)  are  more  easily  seen. 

Make  a  combined  drawing  showing  the  alimentary  canal, 
salivary  glands,  tracheal  trunks,  and  reproductive  organs  in 
position  in  the  body. 

For  a  dissection  of  the  reproductive  organs  in  an  adult 
insect,  see  pp.  41-46. 

The  nervous  system. — Remove  the  alimentary  canal, 
cutting  across  the  oesophagus  near  the  anterior  end  of  the  pro- 
ventriculus.  T\{tbrain  is  composed  of  two  main  lobes  united 
posteriorly  and  lying  above  the  oesophagus.  Beneath  the  brain, 
just  under  the  oesophagus,  lies  the  suboesophageal  ganglion, 
which  is  connected  with  the  anterior  end  of  the  brain-lobes  by 
the  circunioesophagcal  commissures,  nerve-cords  which  together 
with  the  brain  and  suboesophageal  ganglion  form  a  complete 
ring  around    the  oesophagus.      Back  of    the   suboesophageal 


59 

ganglion  is  a  chain  of  four  closely  connected  ganglia.  Lead- 
ing back  from  the  hindmost  of  these  ganglia  are  paired,  but 
closely  opposed,  longitudinal  nerve-cords.  On  these  cords 
in  the  sixth  body-segment  is  another  ganglion,  and  following 
this  are  five  others  similar  to  it,  each  lying  over  the  center  of 
the  sternal  part  of  a  segment.  These  ventral  ganglia,  from 
the  suboesophageal  back,  and  the  connecting  longitudinal 
commissures  constitute  the  ventral  ?ierve  chain  which  with  the 
brain  and  circumoesophageal  ganglia  compose  the  central 
nervous  system  of  the  insect.  In  addition  to  this  central  sys- 
tem there  is  another  smaller  system,  the  sympathetic  nervous 
system,  which  we  shall  not  study  in  this  elementary  dissection. 
Each  ganglion  of  the  ventral  chain,  behind  the  suboesophageal 
ganglion,  gives  off  four  very  conspicuous  nerves ;  one  on 
each  side  arising  from  the  middle  of  the  ganglion  going  to 
the  muscles  of  the  body-wall,  and  another  arising  from  the 
anterior  end  of  the  ganglion  going  to  the  viscera.  The  last 
ganglion  lying  in  the  antepenultimate  body-segment,  in  ad- 
dition to  the  four  lateral  trunks,  gives  off  from  its  posterior 
part  two  large  divergent  ones  running  backwards  to  the  two 
following  segments.  The  brain  and  suboesophageal  ganglion 
give  off  nerves  to  the  organs  of  the  head. 

Make  a  drawing  of  the  nervous  system. 

The  muscular  system. — Along  each  side  of  the  dorsal 
and  ventral  median  line  of  the  body  is  a  wide  band  of  longi- 
tudinal muscles.  The  most  conspicuous  fibers  reach  from 
the  anterior  to  the  posterior  border  of  each  segment,  but  the 
others  reach  from  either  end  to  the  middle,  while  others  ex- 
tend from  the  middle  of  one  segment  to  the  middle  of  the 
preceding  or  following  segment,  while  still  others  are  attached 
to  various  points  of  the  body-wall  between  the  attachments 
of  the  sets  already  mentioned.  Finally,  there  is  an  inner- 
most set  of  lateral  transverse  muscles  in  the  anterior  half  of 
each  segment. 


6o 

Make  a  drawing  showing  the  complete  musculation  of  two 
successive  segments. 

The  circulatory  system. — Cut  a  second  specimen  open 
longitudinally  along  the  median  line  of  the  venter,  reserving 
the  first  specimen  for  some  later  work.  Pin  out  the  cut 
edges.  Note  again  the  general  disposition  of  the  body  or- 
gans so  far  examined.  Examine  again  the  reproductive  or- 
gans ;  the  specimen  may  be  of  the  other  sex  from  that  pre- 
viously studied.     Remove  the  alimentary  canal. 

The  dorsal  vessel  or  heart  is  a  slender,  delicate,  membranous 
tube  composed  of  a  number  of  successive  parts  or  chambers 
lying  along  the  median  line  of  the  back.  To  see  this  well 
cut  out  the  median  dorsal  strip  of  body-wall  carrying  the 
heart  and  transfer  it  to  a  glass  slide.  Cover  with  water  and 
examine  first  under  the  simple  microscope  and  then  under 
the  low  power  of  the  compound  microscope.  It  will  be  dis- 
tinctly seen  that  toward  the  middle  of  each  segment  from 
the  last  to  the  third  inclusive,  the  tube  becomes  dilated, 
forming  a  chamber,  and  in  most  of  these  chambers,  except 
the  last,  a  pair  of  internal  valves  may  be  seen.  From  the 
most  anterior  chamber  a  straight,  tapering  tube,  the  aorta, 
runs  forward  into  the  head,  where  it  ends  by  dividing  into 
branches  which  can  be  followed  for  but  a  short  distance,  ap- 
parently fading  out  completely.  There  are  no  other  blood- 
vessels in  the  body. 

On  each  side  of  each  chamber  may  be  noted  a  fan -shaped 
group  of  very  delicate  muscle  fibers,  apparently  attached  to 
the  sides  of  the  chamber,  and  called  the  wing  muscles  of  the 
heart.  The  convergent  outer  ends  of  these  muscles  are  at- 
tached to  the  body-wall  on  the  line  of  the  median  constric- 
tion in  each  segment.  These  muscles  really  lie  in  a  thin 
membrane  which  forms  a  sort  oi pericardial  membrane  enclos- 
ing a  sinus  on  each  side  of  the  heart  and  stretching  across 
from  these  lateral  sinuses  to  the  body-wall  as  a  septum  or 


6i 

diaphragm.  This  membrane  is  attached  to  the  heart  on  its 
dorsal  and  its  ventral  surface.  The  membrane  and  sinuses 
can  be  especially  well  seen  in  cross  sections  of  the  body. 

For  an  account  of  the  circulation  in  insects  see  the  Cam- 
bridge Natural  History,  Vol.  V.,  pp.  132-136. 

The  histoblasts  of  wings  and  legs. — Returning  to  the 
first  specimen  (that  opened  along  the  dorsum)  carefully  re- 
move the  muscle  fibers  from  the  body-wall  of  the  three  front 
(thoracic)  segments  of  the  body,  not  including  the  head.  Be 
careful  not  to  remove  certain  small  whitish  bud-like  bodies 
lying  between  the  muscles  and  the  body-wall.  In  specimens  of 
sufficient  age  the  histoblasts  (or  i/naginal  buds  or  imaginal  discs 
as  variously  called)  of  the  wings  and  legs  of  the  adult  fly  and 
of  the  external  prothoracic  respiratory  tubes  may  be  seen  as 
small  sac-  or  bud-like  bodies  lying  against  and  attached  to 
the  inner  surface  of  the  body-wall  of  the  thoracic  segments. 
There  are  two  pairs  of  these  imaginal  buds  in  each  thoracic 
segment  corresponding  respectively  to  the  prothoracic  legs 
of  the  imago  and  prothoracic  respiratory  tubes  of  the  pupa, 
the  meso-thoracic  legs  and  wings  of  the  imago,  and  the  meta- 
thoracic  legs  and  halteres  of  the  imago.  The  study  of  the 
morphology  and  development  of  these  imaginal  buds  is  too 
difficult  to  be  referred  to  here.  It  is  sufficient  to  know  that 
the  legs  and  wings  of  the  fly  begin  thus  to  develop  under  the 
surface  of  the  body  and  continue  this  internal  development 
until  the  larva  changes  into  a  pupa.  These  buds  may  be 
seen  to  be  intimately  connected  with  the  thoracic  skin,  and 
are,  in  fact,  actual  invaginated  parts  of  this  skin. 

The  head  and  its  appendages. — After  finishing  the  dis- 
section of  the  internal  organs  remove  the  head  entirely  from 
the  rest  of  the  specimen  and  examine  with  simple  microscope. 
Each  of  the  short  antenncz  arises  from  a  small  lobe  on  the  plate 
covering  the  top  of  the  head.  This  plate  is  long,  tapering  and 
decurved  behind.     It  is  united  along  the  anterior  parts  of  its 


62 

sides  with  lateral  plates,  while  the  anterior' margin  is  re- 
entrant receiving  the  smaller  end  of  the  pear-shaped  labrum. 
The  distal  part  of  this  sclerite  is  membranous  except  for  two 
lateral  chitinizations.  Posteriorly  it  is  fused  with  the  epicra- 
nial plate.  The  lateral  plates  are  each  oval  and  shell-shaped, 
having  their  anterior  lower  angles  produced  forward  and 
united  with  each  other.  The  single  process  thus  formed  pro- 
jects forward  and  curves  upward  between  the  faces  of  the 
posterior  jaws.  The  tips  are  provided  with  graduated  teeth. 
In  front  of  each  lateral  plate  is  a  narrow  dorso-ventral  scle- 
rite carrying  the  jaws.  The  anterior  ones,  mandibles,  are 
large,  strong,  toothed  terminally  and  provided  on  the  inner 
side  with  a  large,  softer,  movable  lobe.  The  posterior  jaws, 
maxillcB,  are  less  strongly  chitinized  than  the  mandibles. 
They  are  fiat,  and  each  is  provided  at  its  outer  angle  with 
several  papilla-like  processes. 


CHAPTER  V. 

THE   EXTERNAL   ANATOMY   OF   A   BEETLE. 
Pterostichus  californicus. 

With  the  knowledge  of  the  external  anatomy  of  the  locust 
as  a  basis  the  student  may  successfully  attempt  to  examine 
comparatively  some  of  the  various  conditions  of  the  body 
exhibited  among  different  orders  of  insects.  With  the  varied 
habits  of  insects  there  are  necessarily  correlated  various 
modifications  of  structure,  internal  and  external.  The  modi- 
fications of  the  external  structure  are  those  taken  special 
cognizance  of  and  used  in  the  present  analytical  tables  and 
keys  for  insect  classification,  and  must  be  studied  to  some 
degree  before  determination  of  insect  forms  can  be  done  in- 
telligently. The  study  of  insect  anatomy  in  a  ccmparative 
way  will  also  give  the  student  an  understanding  of  the  sig- 
nificance of  homology  and  specialization. 

As  an  example  of  simple  work  of  this  character  which 
may  be  undertaken  by  the  student,  the  external  anatomy  of 
a  beetle  (order  Coleoptera)  may  be  studied. 

The  peculiarly  flattened  form  of  many  insects,  by  which 
the  lateral  aspects  of  thorax  and  abdomen  are  reduced  to  a 
mere  ridge  or  margin,  is  accompanied  by  a  change  in  the 
position  of  many  of  the  body  sclerites,  in  particular  the 
pleural  sclerites  of  the  thorax.  This  condition  is  well  ex- 
emplified among  the  predaceous  ground-beetles  {Carabida) 
and  almost  any  species  may  be  selected  for  illustration.  We 
have  chosen  the  species  Pterostichus  cali/ornicus,  as  the  repre- 
sentative of  a  widely  spread  genus,  and  the  description  fol- 

63 


64 

lowing  applies  especially  to  this  form  ;  however,  the  notes 
will  serve  as  a  guide  for  the  examination  of  any  member  of 
the  genus. 

The  meso-  and  metathoracic  segments  are  closely  joined 
to  each  other  and  to  the  abdomen.  The  prothorax  is  freely 
movable  and  is  constricted  at  its  articulation  with  the  meso- 
thorax,  so  that  it  appears  to  form  all  of  the  second  or  tho- 
racic region  of  the  body.  The  insertion  of  the  hinder  two 
pairs  of  legs,  however,  shows  that  part  of  what  at  first 
glance  appears  to  belong  entirely  to  the  abdominal  region  of 
the  body  really  belongs  to  the  thorax.  The  body-wall  is 
very  strongly  chitinized,  the  body  being  enclosed  in  a  veri- 
table coat  of  armor.  The  head  projects  horizontally  from 
the  body  instead  of  hanging  vertically  across  the  front,  as 
with  the  locust,  and  the  flattening  of  the  body  is  evident  in 
all  regions,  head,  thorax,  and  abdomen. 

PARTS   OF   THE    HEAD. 
THE    FIXED    PARTS    OF    THE    HEAD. 

The  fixed  *  parts  of  the  head  are  fused  so  as  to  form  a 
strong  and  rigid  box,  which  is  elongated  and  flattened. 

Epicranium. — The  epicranium  bears  on  its  cephalic  por- 
tion two  impressed  lines  which  run  cephalad  until  they  meet 
the  transversal  clypeal  suture,  the  suture  separating  the  cly- 
peus  from  the  epicranium.  f  Laterad  of  each  of  the  impressed 
lines  on  the  epicranium  there  is,  forming  the  dorso-lateral 
margin  of  the  head,  a  sharp  ridge  called  the  frontal  ridge, 
which    runs   cephalad    from    the    dorsal  margin  of   the  eye. 

"The  "head-capsule"  of  this  beetle  is  very  strongly  chitinized  and  deep 
black  in  color.  To  soften  and  partly  bleach  the  head,  so  that  the  fixed  parts 
may  be  readily  determined,  the  student  must  boil  the  head  for  some  time  in 
caustic  potash  (KOH). 

t  The  epicranium  of  the  beetle,  like  that  of  the  locust,  is  a  compound  sclerite, 
being  composed  of  the  fused  true  epicranium  and  front. 


65 

The  antennae  arise  just  below  this  frontal  ridge  in  a  short, 
rounding  groove  running  cephalad  from  the  eye.  On  the 
•epicranium  just  above  each  compound  eye  are  two,  long 
hairs  arising  from  distinct  pits.  These  pits  are  called  seiiger- 
ous  punctures.  Similar  punctures  and  hairs  are  found  also 
near  the  lateral  margins  of  the  clypeus. 

Clypeus. — The  clypeus  is  broader  than  long,  and  projects 
cephalad  between  the  bases  of  the  mandibles.  Projecting 
cephalad  from  the  cephalic  margin  of  the  clypeus,  is  the  sub- 
quadrangular  labrum,  with  its  distal  margin  slightly  concave 
outwardly. 

Compound  eyes. — The  compound  eyes,  on  the  lateral  mar- 
gins of  the  head,  are  comparatively  small. 

Ocelli. — There  are  no  ocelli. 

Genac. — The  portions  of  the  epicranium  below  the  eyes 
and  antennas  are  the  gence  and  each  projects  cephalad,  latero- 
ventrad  of  the  base  of  the  mandibles,  as  a  thin  tapering 
tongue  curving  inward  slightly  at  its  tip.  Below  this  pro- 
jecting process,  the  gena  presents  a  rounded  emargination, 
and,  filling  in  the  emargination,  may  be  seen  the  basal  por- 
tion of  the  maxillge.  The  genae  form,  with  portions  of  the 
occiput,  the  lateral  portions  of  the  ventral  surface  of  the 
head. 

Occiput. — The  occiput,  although  fused  with  the  epicra- 
nium to  form  the  firm  head-box,  is  plainly  separated  from  the 
epicranium  on  the  dorsal  and  lateral  portions  of  the  head  by 
an  impressed  line,  which  fades  out  on  the  lateral  portions  of 
the  ventral  surface  of  the  head,  so  that  the  postgenal  and 
occipital  regions  cannot  here  be  distinguished. 

Gula. — Forming  the  mesal  third  of  the  ventral  aspect  of 
the  head,  slightly  widening  caudad,  and  expanding  at  its 
cephalic  extremity  to  a  narrow,  transversal  bar,  which  pro- 
jects laterad  to  the  genal  emargination,  is  the  gula,  one  of 
the  head  sclerites,  which  is  wanting  or  is  fused  with  the  sub- 


66 

mentum  in  the  head  of  the  locust.  The  gula  is  usually  a 
well  developed  sclerite  among  beetles.  The  sutures  separat- 
ing it  on  either  side  from  the  contiguous  portions  of  occiput 
and  epicranium  (postgena)  are  called  the  giilar  sutures. 

Make  a  drawing  of  the  ventral  aspect  of  the  head,  show- 
ing the  skeletal  parts  described,  and  also  what  may  be  seen 
of  the  mouth-parts  in  situ. 

THE    APPENDAGES    OF    THE    HEAD. 

Antennas. — The  ante nnce  are  filiform,  and  ii-segmented  ; 
the  third  segment  is  the  longest  one.  The  proximal  three 
segments  are  glabrous,  and  the  second  and  third  bear  each 
two  or  three  longish  hairs  near  their  distal  end.  The  re- 
maining eight  segments  are  finely  pubescent.  In  addition 
each  of  these  eight  bears  a  few  longer  hairs  at  its  distal  end. 

Mouth-Parts. 

The  mouth-parts  are  fitted  for  biting  and  are  in  general 
similar  to  the  mouth-parts  of  the  locust. 

Labrum. — The  labrum  has  been  described  already  as  a 
part  of  the  skull. 

Mandibles. — The  mandibles  are  rather  long,  and  taper 
distad  to  a  sharp,  curving  tooth.  They  bear  on  their  sharp, 
cutting,  inner  margin,  near  the  base,  a  few,  small,  blunt 
teeth,  and  their  outer  face  presents  a  broad,  shallow  groove 
or  furrow  called  the  mandibular  scrobe.  Make  a  drawing  of  a 
mandible. 

Maxillae. — The  maxillce  differ  especially  from  those  of 
the  locust  by  the  presence  of  an  additional  sclerite,  the  sub- 
galea,  by  the  side  of  the  stipes,  as  if  the  stipes  were  divided 
by  a  longitudinal  suture.  The  cardo  is  large,  and  broadly 
club-shaped  ;  the  median  portion  of  the  maxilla  is  composed 
of   three   sclerites,  the  stipes^  palpifer  and   subgalea.     These 


6y 

three  sclerites  may  be  distinguished  when  the  maxilla  is 
viewed  from  the  dorsal  aspect  by  the  following  characters; 
the  palpifer  lies  above  the  distal  two-thirds  of  the  stipes, 
and  also  overlaps  part  of  the  subgalea.  It  is  elongate,  sub- 
triangular  in  outline  with  apex  directed  toward  the  lacinia. 
From  it  arises  the  four-segmented  palpus,  and  it  also  bears 
near  the  origin  of  the  palpus  a  single,  conspicuous,  long 
bristle.  The  stipes  as  seen  from  above  is  elongate  and 
rather  slender,  with  the  basal  extremity  widened.  It  lies 
laterad  of  the  large  subgalea,  which  forms  the  inner  or  mesal 
half  of  the  median  portion  of  the  maxilla.  From  the  sub- 
galea the  two  lobes,  galea  and  lacinia^  of  the  maxilla  arise. 
The  galea  is  slender,  elongate,  distinctly  two-segmented,  and 
palpiform  in  character.  The  lacinia  is  strongly  chitinized, 
and  is  beset  on  its  inner  face  with  strong  and  long,  curved 
spines,  and  on  its  dorsal  aspect  with  many,  weaker  hairs. 
It  bears  on  its  distal  end  a  strong  tooth  or  curved  tip,  known 
as  the  digitus. 

Make  a  drawing  of  the  dorsal  aspect  of  a  maxilla. 

Labium. — The    labium   is   separated   from    the   cepnalic 
transverse    portion   of    the   gula    by  a  straight,    transverse 
suture.     The   submentum    is    large,    strongly  chitinized,  and 
with  its  lateral  portions  appearing  as  broad,  expanded  lobes 
separated    by    a    broad   and    deep,    cephalic    emargination 
Bordering  this  emargination   is  the  narrow  curving  t/ie/itum 
with    a    median    forward-projecting,    two-pointed    portion 
From  the  elongated,  subcylindrical,  forward-projecting  pal 
pigers  arise  the   three-segmented  labial  palpi,  the  first  seg 
ments  of  which  are  very    short.     Also   projecting  forward 
from    the    mentum    is   the   ligula,  composed  of  a  dorsal  or 
inner,  delicate,  transparent,  membranous  part,  which  divides 
at  its  tip  into  two,  slender,  tapering  projections,  the  para- 
glosscE,  and  a  ventral  or  outer,  chitinized,  undivided  portion, 
t\\Q  glossa.     The  tip  of  the  glossa  is  truncate,  and  bears  two, 


68 

long,  strong  hairs.  Each  paraglossa  lies  slightly  laterad  of 
the  distal  half  of  the  glossa.  The  entire  ligula  arises,  not 
from  the  cephalic  margin  of  the  mentum,  but  from  its  inner 
or  dorsal  face,  and  it  may  be  that  its  parts  are  not  homolo- 
gous with  the  terminal  lobe  (ligula)  of  the  locust's  labium, 
but  that  one  or  perhaps  both  parts  are  continuous  with  the 
lining  of  the  mouth-cavity  ;  in  which  case  they  would  be 
homologous  with  the  hypopharynx  of  the  locust's  mouth. 

Make  a  drawing  of  the  ventral  (outer)  aspect  of  the 
labium. 

PARTS   OF   THE   THORAX. 
PROTHORAX. 

Dorsal  aspect. — The  pronotu?n  is  not  divided  into  differ- 
ent sclerites,  but  appears  as  a  single,  firm,  convex  plate,  bear- 
ing a  median  impressed  line,  and,  laterad  of  this  line,  on 
each  side  near  the  caudal  margin,  a  short,  linear  depression. 
At  the  acute  lateral  margins,  the  pronotum  is  inflexed, 
extending  a  little  distance  ventro-mesad  on  the  ventral 
(pleural  s.  str.)  aspect  of  the  body.  This  inflexed  portion  is 
often  called  Xhe  prothoracic  epipleura. 

Ventral  aspect. — The  sternum  and  the  true  pleural  scle- 
rites or  "  side  pieces,"  together  form  the  ventral  aspect  of 
the  prothorax. 

Sternum. — The  sternum,  constituting  the  median  region  of 
this  aspect,  is  irregularly  saddle-shaped,  with  a  caudad-pro- 
jecting  tongue  between  the  coxal  cavities.  This  tongue  after 
reaching  the  caudal  margins  of  the  coxae  bends  at  right 
angles  and  projects  dorsad,  the  end  expanding  slightly  into 
two  dorso-laterad  projecting  points,  which  meet  a  ventro- 
mesad  projecting  point  of  the  epimeron  on  each  side,  and  thus 
form  part  of  the  enclosing,  caudal  boundaries  of  the  coxal 
cavities. 


69 

Episternum. — The  episterfium,  a  large  rhomboidal  sclerite, 
constitutes  most  of  the  body-wall  between  the  sternum  and 
the  epipleurae. 

Epimeron. — Separated  from  the  caudal  extremity  of  the 
episternum  by  a  distinct  suture,  is  the  narrow,  curving 
epimeron,  whose  expanded  mesal  extremity  presents  two, 
pointed,  curving  processes,  which  enclose  the  coxal  cavity 
laterad  and  caudad.  The  meeting  of  the  epimeron  and 
sternum  caudad  of  the  coxal  cavity  technically  closes  it,  or 
makes  it  entire ;  if  these  two  sclerites  do  not  meet,  as  is 
often  the  case  among  beetles,  and  the  cavity  is  bounded 
caudad  simply  by  membrane,  the  cavity  is  said  to  be  opeti. 
If  there  is  no  caudal  tongue  projecting  between  the  cavities, 
they  are  said  to  be  confluent ;  when  separated,  as  in  the  speci- 
men in  hand,  by  this  tongue,  they  are  technically  separate. 

MESOTHORAX. 

Dorsal  aspect. — When  the  wing-covers  are  folded  the 
only  part  of  the  mesonotum  visible  is  the  small,  median,  tri- 
angular or  shield  -  shaped  portion  of  the  scutellum.  By 
spreading  apart  or  breaking  away  the  wing-covers,  the  lat- 
eral membranous  portions  of  the  scutellum  may  be  seen,  as 
well  as  the  scutum ;  the  median  part  of  the  scutum  is 
strongly  chitinized  and  the  lateral  parts,  weakly  chitinized. 
The  postscutellum  also  may  be  distinguished  as  a  narrow, 
weakly-chitinized,  curving  bar,  running  laterad  on  each  side 
just  in  front  of  the  caudal  apex  of  the  scutellum.  The 
prcBSCutum  is  represented  merely  by  a  thin,  transversal  strip 
of  membrane. 

Ventral  aspect. — As  with  the  prothorax  the  ventral 
aspect  of  this  segment  is  composed  of  the  sternum  and  the 
pleural  sclerites. 

Mesosternum. —  The  fnesosternum  is  plainly  set  off  by 
sutures.     Its   caudal    margin    has  a  broad,  median    tongue, 


70 

which  projects  caudad  between  the  coxal  cavities,  and  is 
angularly  eraarginated  at  its  tip.  Laterad  of  this  tongue  are 
two  rounding  emarginations,  for  the  reception  of  the  coxse. 
Bounding  each  coxal  cavity  laterad  is  a  caudad-projecting 
portion  of  the  sternum.  Cephalad  the  sternal  sclerite  tapers 
somewhat,  and  the  cephalic  margin  is  narrowly  truncate. 
A  narrow,  collar-like  cephalic  margin  which  fits  into  the  pro- 
thorax,  is  separated  from  the  rest  of  the  sternum  by  a  slight 
carina  or  elevated  line. 

Episternum. — The  pleural  sclerites  are  distinct  ;  the  epi- 
sternum  is  large,  angularly  concave,  and  does  not  reach  the 
coxa.  It  bears  near  its  cephalic  margin  two,  transversal 
raised  lines  or  carinae,  one  of  which  is  a  continuation  of  the 
collar-making  carina  of  the  sternum.  Like  the  sternum,  the 
cephalic  margin  of  the  episternum  fits  into  the  prothorax. 
The  lateral  margin  is  angularly  inflexed  along  its  entire 
length,  as  is  the  case  with  all  the  pleural  sclerites.  The 
narrow,  inflexed  portion  is  covered  when  the  wing-covers 
are  closed  by  the  inflexed,  lateral  margin  of  the  wing- 
covers. 

Epimeron. — The  epimeroji,  lying  along  the  caudal  margin 
of  the  episternum,  is  a  narrow,  transversal  sclerite.  Its 
mesal  extremity  does  not  reach  the  coxal  cavity,  but  lies 
contiguous  to  the  lateral  margin  of  the  metasternum. 

METATHORAX. 

Dorsal  aspect. — When  the  elytra  are  closed  the  meta- 
notum  is  completely  covered  and  invisible.  By  removal  of 
the  elytra,  the  metanotum  is  revealed  as  a  narrow  transver- 
sal bar,  on  the  surface  of  which  a  number  of  sutures  and 
elevated  and  depressed  lines  are  to  be  seen.  The  work  of 
distinguishing  the  various  component  sclerites  of  the  meta- 
notum cannot  be  done  satisfactorily  by  the  elementary 
student.  .There  is  a  conspicuous  depression.or.  groove  ex^ 


71 

tending  caudo-cephalad  along  the  middle  of  the  back,  with 
strongly  chitinized  margins  which  project  slightly  mesad 
over  the  depression.  On  the  inner  surface  of  the  elytra, 
near  the  base  of  the  mesal  margins,  there  are  two,  slight, 
projecting  processes.  These  small  processes  have  strong, 
acute  margins,  which  project  slightly  laterad.  When  the 
elytra  are  closed,  the  raised  processes  fit  into  the  groove  of 
the  metanotum,  and  the  laterad-projecting  margins  of  the 
processes  lie  under  the  mesad-projecting  margins  of  the 
groove,  the  whole  structure  forming  a  means  for  the  firm 
holding  of  the  elytra  over  the  dorsum  of  the  body.  The 
firm  holding  of  the  elytra  is  further  aided  by  the  inflexed 
lateral  margins  and  by  the  close  dovetailing  of  the  mesal 
margins  along  the  middle  of  the  back. 

Ventral  aspect. — As  in  the  other  thoracic  segments  this 
includes  both  the  sternum  and  the  pleural  sclerites. 

Metasternum. — The  metasternum  is,  as  the  mesosternum, 
best  described  as  saddle-shaped.  It  has  a  rather  broad, 
blunt  tongue,  projecting  cephalad  between  the  mesocoxae  to 
meet  the  caudad-projecting  tongue  of  the  mesosternum.  It 
presents,  also,  an  acute-angle  process,  projecting  caudad 
between  the  cephalic  halves  of  the  metacoxae.  The  "  sad- 
dle-flaps," or  lateral  lobes  of  the  metasternum  expand  later- 
ad, and  their  cephalic  margins,  concavely  rounded,  form  the 
caudal  boundaries  of  the  mesocoxal  cavities.  There  is  a 
line  or  suture  running  transversely  across  the  metasternum 
near  the  caudal  margin  which  does  not  reach  the  lateral 
margins.  That  portion  of  the  metasternum  caudad  of  this 
suture  is  called  the  antecoxal piece  of  the  metasternum. 

Episternum. — The  rhomboidal  episternum  is  the  largest  of 
the  pleijral  sclerites. 

Epimeron. — The  trapezoidal  epimeron,  though  smaller  than 
the  episternum,  is  broader,  and  more  conspicuous  than  that 
of  either  of  the  other  thoracic  segments. 


72 

Make  a  drawing  of  the  ventral  aspect  of  the  entire  thorax, 
including  the  legs  of  the  left  side. 

APPENDAGES    OF    THE    THORAX. 

The  hind  wings  are  wanting  in  this  beetle.  This  is  ex- 
ceptional, however,  among  beetles,  the  hind  wings,  mem- 
branous and  with  a  few  strong  veins,  being  usually  well- 
developed,  and  differing  from  the  wings  of  most  insects  in 
being  folded  transversely  as  well  as  longitudinally  when  the 
insect  is  at  rest. 

The  fore-wings  are  very  strongly  chitinized  and  thick- 
ened, and  are  called  elytra  or  wing-covers.  When  the  beetle 
is  at  rest  the  elytra  fit  closely  over  the  dorsal  aspect  of  the 
meso-  and  metathorax  and  abdomen,  protecting  the  abdo- 
men and  hind  wings,  which  (when  present,  as  in  most  bee- 
tles) lie  folded  over  the  metathorax  and  abdomen  and 
beneath  the  wing-covers.  The  elytra  are  articulated  with 
the  body  so  as  to  be  freely  movable,  being  outspread  when 
the  beetle  is  in  flight.  The  basal  or  articulating  parts  of 
the  elytra  lie  just  ventro-laterad  of  the  lateral  margins  of 
the  scutellum.  The  expanded  flap  or  wing-like  parts  pre- 
sent a  series  of  sub-parallel,  longitudinal,  impressed  lines, 
and  the  lateral  margins,  termed  epipleura,  are  inflexed  over 
the  dorso-lateral  margins  of  the  body.  This  inflexed  con- 
dition of  the  margins  does  not  extend  quite  to  the  tips  of 
the  elytra,  but  disappears  at  a  point  where  the  margin  ap- 
pears to  be  interi-itpted.  On  the  inner  surface  of  each  ely- 
tron near  the  lateral  margin  there  is  a  distinct  longitudinal 
fold  ox  plica. 

PARTS    OF    THE    ABDOMEN. 

The  abdomen  is  composed  of  a  number  of  very  much 
flattened  segments  ;  and  its  dorsal  surface  or  tergum  is  com- 
pletely covered  by  the  elytra  when  they  are  closed.     On  the 


73 

ventral  surface,  six  strongly-chitinized  sterna  may  be  count- 
ed. The  first  (basal)  sternum  is  completely  divided  by  the 
coxal  cavities,  so  that  it  appears  as  two  triangular  pieces, 
lying  laterad  of  the  coxae.  The  cephalic  margin  of  the  sec- 
ond sternum  is  emarginated  on  each  side  of  the  meson  by 
the  coxal  cavities,  so  that  the  mesal  part  of  the  cephalic 
margin  appears  as  an  acute,  cephalad-projecting  process. 
The  third,  fourth  and  fifth  sterna  are  of  about  equal  length 
(caudo-cephalic),  the  sixth  being  longer  and  having  its  cau- 
dal  margin  roundly  pointed.  The  first,  second  and  third 
sterna  are  connate  (firmly  united,  not  movable  on  each 
other),  although  the  sutural  lines  are  distinct.  All  of  the 
sterna  have  strongly  chitinized,  lateral  margins,  which  pro- 
ject somewhat  dorsad,  and  then  are  narrowly  inflexed  over 
the  dorso-lateral  margin  of  the  abdomen.  There  are  seven 
terga,  the  tergal  aspect  corresponding  to  the  sixth  sternum 
being  unequally  divided  by  a  transversal  suture,  producing 
thus  an  additional  small  tergum.  All  of  the  terga  are  mem- 
branous except  the  sixth  and  seventh,  which  are  chitinized, 
and  are  known  respectively  as  the  propygidium  and  pygidiutn. 
The  propygidium  is  coarsely  punctulated,  but  the  surface  of 
the  pygidium  is  smooth.  Each  tergum  except  the  seventh 
bears  a  pair  of  spiracles,  located  near  the  cephalo-lateral 
angles  of  the  terga.  Between  the  lip-like  caudal  margin  of 
the  pygidium  and  the  sixth  sternum  there  is  a  transversal 
fissure,  in  which  lie  the  anal  and  genital  openings. 


CHAPTER    VI. 
THE   MOUTH-PARTS   OF  INSECTS. 

The  study  of  the  mouth-parts  of  insects  is  of  special  in- 
terest and  importance  because  of  the  admirable  illustration 
of  the  principle  of  homology  presented  by  the  mouth-parts, 
because  in  the  classification  of  insects  great  importance  is 
assigned  to  the  mouth-structure,  and  finally  because  of  the 
significance  of  the  structural  character  of  the  mouth  in  the 
study  of  the  habits  and  economic  relations  of  insects. 

The  mouth-parts  of  the  locust,  the  cockroach,  and  the 
beetle  have  already  been  studied:  they  represent  the  biting 
type  of  insectean  mouth-parts.  The  student  is,  therefore, 
already  acquainted  with  the  component  parts  of  the  mouth, 
and  with  their  character  in  the  biting  type.  The  mouth- 
parts  of  many  insects,  however,  are  not  of  the  strictly  biting 
type,  but  are  modified  to  form  an  elongate  tubular  beak  or 
proboscis  used  for  sucking  liquid  food,  or  are  modified  to 
form  a  combination  of  the  biting  and  sucking  types.  This 
modification  of  the  more  generalized  biting  type  varies  in 
the  various  insect  orders  possessing  "sucking  mouth-parts." 
As  a  beginning  in  the  comparative  study  of  the  sucking  type, 
the  mouth-parts  of  a  short  series  of  insects,  representing  sev- 
eral important  orders,  may  be  examined. 

In  the  examination  of  the  mouth-parts  dried  specimens  can 
be  advantageously  employed.  Remove  the  head  from  the 
dried  insect  and  boil  it  in  dilute  potassium  hydrate  (KOH)  to 
soften  and  partially  bleach  the  chitinous  parts.  The  length 
of  time  of  boiling  will  depend,  of  course,  upon  the  degree  of 

74 


75 

Qhitinization  and  coloration  of  the  parts.  The  head  should 
then  be  washed  in  water  and  removed  to  a  watch  glass  con- 
taining water.  The  mouth-parts  can  now  be  examined  injitti 
and  finally  readily  dissected  apart  by  means  of  dissecting 
needles  and  forceps. 

The  parts  can  be  temporarily  mounted  in  glycerine,  or  if 
permanent  mounts  are  desired,  the  parts  can  be  mounted  in 
glycerine  jelly.  Carry  from  the  water  directly  into  the  jelly. 
For  mounting  in  Canada  balsam  the  parts  must  be  thoroughly 
dehydrated  by  carrying  through  successive  strengths  of  alco- 
hol up  to  absolute,  and  then  clearing  in  xylol  or  other  clear- 
ing oil. 

BITING    AND    SUCKING    MOUTH-PARTS. 

In  the  Hymenoptera,  the  mandibles  retain  their  function 
of  biting,  while  the  maxillae  and  labium  unite  to  form  an  ap- 
paratus for  lapping  or  sucking  liquids.  Two  examples  of 
this  condition  of  mouth-parts  fitted  for  biting  and  sucking 
may  be  examined  :  a  wasp,  in  which  the  maxillae  and  labium 
are  somewhat  elongated  and  fitted  for  lapping  ;  and  a  honey- 
bee, in  which  the  maxillae  and  labium  are  much  elongated 
and  fitted  for  sucking. 

MOUTH-PARTS    OF    THE    WHITE-FACED    HORNET. 

Vespa  jfiaculata  ;  order  Hymenoptera. 

Because  of  the  considerable  membranous  and  fleshy  tissue 
of  the  mouth-parts,  bleaching  in  KOH  should  not  be  carried 
far  ;  a  minute  or  two  of  boiling,  sufficient  for  softening,  will 
do.  In  fact,  simply  softening  in  warm  water  is  perhaps  safer. 
.  The  mouth-parts  of  the  wasps  and  bees  are  so  thoroughly 
united  at  the  base  by  the  development  of  the  pharyngeal 
skeleton  and  membrane  that  a  considerable  tearing  of  tissue 
is  necessary  to  separate  the  parts.     The  mouth-structure  as 


1^ 

a  whole  should  be  carefully  examined  before  the  parts  are 
dissected  out. 

In  the  study  of  the  mouth-parts  of  insects  the  student 
should  bear  in  mind  that  the  labrum,  although  in  position 
and  use  actually  one  of  the  mouth-parts,  differs  morphologic- 
ally from  the  mandibles,  maxillae  and  labium  in  not  being  a 
modified  pair  of  head  appendages. 

Labrum. — The  labrum  is  short  and  broad,  and  is  immov- 
ably fused  with  the  clypeus, 

Epipharynx. — Directly  underneath  the  labrum  is  the  well- 
developed  elongate  strap-like  epipharynx.  It  is  fleshy  and 
membranous  and  bears  numerous,  spiny  hairs. 

Mandibles. — The  mandibles  are  large  and  toothed.  When 
they  are  closed  one  overlaps  the  other  to  a  considerable 
extent. 

Maxillae. — The  maxillae,  although  of  the  generally  simple 
character  of  the  biting  type,  show  some  rather  confusing 
modifications.  The  cardo  is  strongly  chitinized,  distinct, 
rather  large  and  subclavate  in  shape.  The  stipes  is  large, 
strongly  chitinized  and  is  (like  the  stipes  of  the  beetle's 
maxilla)  partly  divided  into  three  sclerites,  from  one  of  which 
rises  the  small,  slender,  six-segmented  palpus.  The  terminal 
lobes  assume  a  peculiar  character,  the  distinctly  two-seg- 
mented galea  being  large  and  flat,  and  bearing  many  papillar 
hairs.  From  the  large  basal  segment  of  the  galea  there  rises 
a  distinct,  flattish  lobe  also  bearing  many  long  papillar  hairs. 
Make  a  drawing  of  a  maxilla. 

Labium. — The  labium  is  a  complex  organ  in  which,  how- 
ever, the  typical  composing  parts  can  be  pretty  readily  dis- 
tinguished. The  submentum  and  mentum  are  fused  to  form 
a  large  strongly  chitinized,  bent,  basal  sclerite.  This  scle- 
rite  is  bent  so  as  to  present  a  strongly  convex  under  (outer) 
surface,  and  a  deeply  concave  upper  (inner)  surface.  This 
deep  concavity  or  furrow  is  filled  with  the  fleshy  and  mem- 


77 

branous  folds  of  the  hypopharyngeal  or  ventral  lining  of  the 
mouth.  There  is  a  certain,  short,  broad,  fleshy  flap  which 
may  be  called  the  hypopharynx.  From  this  basal  sclerite 
(fused  submentum  and  mentum)  arise  the  slender  four-seg- 
mented labial  palpi,  and  the  terminal  lobes.  The  paraglossae 
are  distinct,  thin,  membranous  structures  with  the  basal  por- 
tion well  chitinized  and  with  a  peculiar  button-like  chitinized 
tip.  The  gloss?e  are  fused  at  their  base,  and  show  a  well- 
developed  basal  chitinous  skeleton-plate.  The  membranous 
portions  of  the  glossse  are  also  fused  for  about  half  their  dis- 
tance ;  the  apical  halves,  however,  are  free,  and  each  one 
bears  a  button-like,  chitinized  tip,  like  the  tips  of  the  para- 
glossae. 

Make  a  drawing  of  the  labium. 

Make  a  drawing  of  the  cephalic  aspect  of  the  head  showing 
the  fixed  and  movable  parts. 

MOUTH-PARTS    OF    THE    HONEY-BEE. 

Apis  nielli fica  ;  order  Hymenoptera. 

Most  of  the  bees  in  alcohol  (if  an  alcohol  specimen  is 
used)  will  be  found  to  have  certain  of  the  mouth-parts  pro- 
truding. 

These  parts  are  the  maxillae  and  labium,  united  at  the  base 
and  associated  to  form  a  sucking  proboscis.  Before  the  de- 
tailed examination  of  these  parts  is  begun  the  student  should 
discover  the  labrum  and  mandibles. 

Labrum. — The  labrum  is  small  and  oblong  in  shape  with 
its  laterocephalic  corners  rounded.  The  breadth  (lateral)  is 
about  three  times  its  length  (caudo-cephalic). 

Mandibles. — Partially  concealed  beneath  the  labrum  are 
the  spoon-shaped  mandibles.  With  forceps  or  needle,  press 
the  mandibles  apart  at  their  tips  (press  laterad).  Note  that 
the  mandibles  are  not  toothed,  but  are  rather  paddle  or  spoon- 


73 

like  at  the  tips.  Remove  a  mandible  and  make  a  drawing 
of  it. 

Remove  both  mandibles  and  labrum,  and  grasp  the  re- 
maining protruding  parts  with  forceps  and  carefully  pull 
them  loose  from  the  head.  Wash  while  still  held  in  the  for- 
ceps, and  mount  in  glycerine  on  a  glass  slide.  Before  reading- 
farther  the  student  should  endeavor  to  name  the  various 
parts  presented  before  him  on  the  slide. 

Make  a  drawing  of  the  maxillae  and  labium,  and  name  the 
parts,  tentatively.  Compare  the  result  with  the  notes  fol- 
lowing : — 

Maxillse. — The  parts  of  each  maxilla  present  are  the  car- 
do,  stipes,  galea  (or  lacina  ;  one  of  the  two  is  probably  want- 
ing), maxillary  palpi,  and  possibly  the  palpifer. 

Cardo.— The  cardo,  or  proximal  part  of  the  maxilla,  is  a 
rather  long,  slender,  strongly  chitinized  sclerite,  somewhat 
resembling  a  human  femur  or  thigh-bone  in  shape.  At  its 
proximal  end  it  terminates  in  two  unequal  prongs,  the  point 
of  the  larger  being  bluntly  rounded.  At  its  distal  end 
(articulating  with  the  stipes)  it  expands  club-like. 

Stipes. — The  stipes  is  an  irregular,  elongate  sclerite,  strongly 
chitinized.  Its  proximal  end  is  bluntly  rounded  and  swollen. 
The  stipes  articulates  with  the  proximal  segment  of  the  galea 
(see  below)  by  a  long  diagonal  face. 

Galea. — The  galea  (we  incline  to  believe  this  part  homolo- 
gous with  the  galea  of  the  locust's  maxilla,  rather  than  with 
the  lacinia,  because  of  its  two-segmented  condition)  extends 
distad  from  the  stipes  as  a  tapering  blade-shaped  piece.  It 
is  composed  of  two  segments.  The  proximal  one  is  small 
and  triangular,  articulating  by  the  entire  length  of  one  of  its 
margins  with  the  stipes.  The  distal  segment  or  sclerite  con- 
stitutes the  real  blade-like  portion  of  the  maxilla,  and  nearly 
equals  in  length  the  ligula  and  labial  palpi  (see  below).  Its 
surface   is  unequally  divided  into  two   portions  by  a  subme- 


79 

dian,  dark-brown,  longitudinal  line.  (This  line  may  indicate 
a  coalescence  of  galea  and  lacinia  into  this  one  blade-like 
compound  sclerite.)  This  line  bears  several  hairs,  and  there 
are  scattering  hairs  elsewhere  on  the  sclerite,  especially 
toward  the  distal  end.  Near  the  proximal  end  of  this  distal 
segment  of  the  maxilla,  and  between  the  longitudinal  line 
and  the  outer  margin,  many  two-jointed  papillae  (taste 
organs  ?)  can  be  seen  with  a  high  power. 

AI axillary  palpi. — The  maxillary  palpi  z.x^  minute,  exarticu- 
late,  outward-projecting  pieces,  arising  from  near  the  outer 
end  of  the  suture  separating  the  proximal  from  the  distal 
segment  of  the  galea. 

Labium. — The  parts  of  the  labium  present  are  the  sub- 
mentum,  mentum,  glossa,  paraglossae,  palpifer,  and  palpi. 

Submentum. — The  siibmentum  is  a  small,  shield-like  piece  ; 
its  proximal  end  is  connected  by  two  chitinous  bands,  the 
lora,  with  the  cardo  of  each  maxilla ;  its  distal  end  articulates 
with  the  mentum.  The  submentum  is  rather  feebly  chi- 
tinized. 

Mentum. — The  mentum  is  rather  oblong  in  shape,  with 
rounding  corners,  and  strongly  chitinized. 

Glossa. — Rising  from  the  distal  end  of  the  mentum  is  the 
long  glossa,  which  terminates  in  a  small  transparent  lobe  or 
flabellum.  The  glossa  should  be  carefully  examined  under 
low  and  high  magnification.  Note  the  reticulated  and  hairy 
surface.  The  visible  surface  is  that  of  a  sheath  which  en- 
closes a  slender  flexible  rod,  the  rod  being  probably  con- 
cerned with  the  movements  of  the  organ. 

Paraglossce. — At  each  side  of  the  glossa,  and  rising  from 
near  its  proximal  end  are  two  subtransparent  lobes  or  flaps, 
extending  about  one-fifth  the  length  of  the  glossa.  These 
are  the  paraglossae. 

Palpifers  and  Labial  Palpi. — Lying  just  laterad  of  the  para- 
glossse  and  rising  from  the  distal   end  of  the  mentum  are 


80 

two,  long,  flattened  processes,  composed  of  several  segments. 
The  basal  segment,  which  is  the  largest  and  longest  of  the 
segments,  extends  forward  for  about  one-half  the  length  of 
the  ligula,  and  is  the  palpifer  ;  the  succeeding  three  seg- 
ments compose  the  labial  palpus. 

The  proximal  one  of  these  segments  is  the  largest  and  ap- 
pears to  be  a  direct  continuation  of  the  palpifer,  separated 
only  by  a  narrow  straight  suture  ;  the  remaining  two  seg- 
ments are  very  small. 

Make  a  drawing  of  the  cephalic  aspect  of  the  head  show- 
ing the  fixed  and  movable  parts. 

PIERCING    AND    SUCKING    MOUTH-PARTS. 

Among  the  insects  whose  mouth-parts  are  fitted  exclu- 
sively for  piercing  and  sucking  (or  sucking  alone)  the  man- 
dibles, if  present,  are  modified  to  form  slender  elongate  sty- 
lets or  blades. 

This  is  the  condition  presented  by  the  Hemiptera,  and 
some  of  the  Diptera  ;  with  most  of  the  Diptera  and  ail  of  the 
Lepidoptera  (excepting  Eriocephala)  the  mandibles  are  com- 
pletely lost,  or  are  so  atrophied  as  to  be  functionless.  As 
examples  of  insects  with  strictly  sucking  mouth-parts  the 
student  may  examine  a  Cicada  (Hemiptera),  a  horse-fly  and 
a  house-fly  (Diptera,  one  with  and  the  other  without  mandi- 
bles) and  a  butterfly  (Lepidoptera). 

MOUTH-PARTS   OF    A    CICADA. 

{Cicada  sp.;  order  Hemiptera^ 

The  sucking  beak,  tapering  from  base  to  tip,  will  be 
found,  in  dried  specimens,  usually  appressed  to  the  ventral 
surface  of  the  body  of  the  Cicada. 

Remove  the  head  with  the  beak  from  the  dried  specimen^ 


8i 

and  examine  the  beak  before  dissection.  The  long,  three- 
jointed  labium^  forming  all  of  the  beak  as  seen  superficially, 
is  specially  chitinized  (brown)  near  its  distal  end.  The  dis- 
tal joint  is  the  longest,  and  its  surface  is  sparsely  covered 
with  fine,  whitish  hairs.  The  tip  is  rather  blunt  than  acute. 
A  narrow  channel,  widest  at  its  proximal  end,  runs  along  the 
upper  face  of  the  labium.  In  this  channel,  but  concealed 
by  the  approaching  edges  of  it,  lie  the  mandibles  and  max- 
illae. A  glimpse  of  the  mandibles  and  maxillae  just  at  the 
base  of  the  labium  can  often  be  had.  Above  the  base  of  the 
labium  is  the  minute,  acute-angled  labrum  lying  just  over 
the  entering  mandibles  and  maxillae. 

With  a  dissecting  needle  carefully  break  away  the  head- 
wall  and  muscle  near  the  base  of  the  beak,  especially  dorsad 
and  laterad.  The  bases  of  the  mandibles  and  fnaxillcB  will  be 
discovered  as  small,  strongly  chitinized  (brown),  terminal 
dilations  of  slender,  chitin  rods,  which  run  forward  into  the 
channel  of  the  labium.  Note  the  relative  position  of  the 
two  rods  with  dilated  bases  on  either  side,  and  decide  which 
is  mandible  and  which  maxilla.  (The  rod  lying  slightly 
dorsad  and  laterad  of  the  other  is  the  mandible  ;  the  man- 
dible is  also  thicker  and  larger  than  the  maxilla.)  Trace  the 
slender  chitin  rods  or  stylets  (the  mandibles  and  maxillae) 
into  the  channel  of  the  labium.  Here  they  are  all  closely 
appressed,  the  two  maxillae  specially  so,  so  that  they  can  be 
separated  only  with  difficulty. 

Remove  the  mandibular  and  maxillar  stylets  and  note  the 
channel  in  which  they  naturally  lie.  The  labium  is  more 
strongly  chitinized  along  the  walls  of  the  channel  than  else- 
where, except  at  its  tip. 

Make  a  drawing  of  the  mouth-parts  from  dorsal  view, 
with  the  mandibles  and  maxillae  removed  from  the  channel 
of  the  labium  and  spread  apart. 


^^34- 


82 


MOUTH-PARTS    OF    THE    HORSE-FLY. 

{Tabanus  or  Therioplectes  sp.;  order  Diptera.) 

Among  the  flies  with  piercing  mouth-parts  only  the 
females  possess  mandibles.  It  is  therefore  necessary  to 
select  a  female  horse-fly  (distinguished  from  the  male  by  the 
narrow  space  between  the  eyes  ;  in  the  males  the  eyes  touch 
each  other  for  a  greater  or  less  distance  along  the  dorsal 
aspect  of  the  head). 

The  projecting  mouth-parts  are  conspicuous.  On  super- 
ficial examination  there  may  be  noted  two,  thickened, 
slightly  curving,  horn  or  club-like  processes  (the  maxillary 
palpi)  projecting  above  a  black,  thickened  stalk  or  trunk 
(the  labium),  on  the  dorsal  surface  of  which  lie  several  light 
brown,  slender,  pointed  stylets  (mandibles,  maxillae,  labrum, 
epipharynx,  and  hypopharynx). 

For  the  detailed  examination  of  the  mouth-parts,  the  head 
of  the  fly  should  be  removed  from  the  body,  a  considerable 
part  of  the  head,  laterad  and  caudad,  broken  away  and  the 
remainder,  with  mouth-parts  attached,  boiled  in  KOH  to 
soften  and  bleach. 

The  large  maxillary  palpi  are  two-segmented  ;  the  distal 
segment  is  longer  than  the  basal  one,  and  compressed.  The 
proximal  one  is  subcylindrical,  and  projects  dorso-cephalad, 
so  that  the  large  distal  segment  is  carried  above  the  rest  of 
the  mouth-parts. 

Lying  along  the  dorsal  surface  of  the  large  labial  trunk 
are  six  long,  slender,  pointed  pieces  or  stylets.  The  upper- 
most, unpaired,  flat  piece  is  the  labrum  (or  perhaps  labrum 
and  epipharynx  fused).  It  is  rather  bluntly  tipped  and  is 
the  broadest  of  the  stylets.  The  flat,  smooth,  sharply 
pointed  mandibles  lie  just  above  the  less  strongly  chitinized, 
narrower,  and  finely  marked  maxillce.  Corresponding  some, 
what  to  the  labrum^  but  less  broad  and  strong,  is  the  sixth 


83 

stylet,  an  unpaired  slender  piece  lying  below  the  maxillae. 
This  is  the  greatly  developed  hypopharynx.'^  These  six 
stylets,  labrum,  mandibles,  maxillae,  and  hypopharynx  are 
the  instruments  with  which  the  female  horse-fly  pierces  the 
skin  of  animals  to  get  at  the  blood  ;  the  male  has  no  pierc- 
ing stylets,  and  feeds  on  flower-pollen. 

Beneath  the  grouped  stylets  is  the  long  trunk-  or  probos- 
cis-lik^  labium^  presenting  on  its  upper  surface  a  shallow  fur- 
rpw  in  which  the  stylets  may  be  partially  enclosed,  and  pre- 
senting at  its  distal  extremity  a  conspicuous,  expanded,  disk- 
like part  called  the  labella.  This  terminal  disk  is  believed  by 
some  entomologists  to  be  composed  of  the  greatly  modified 
labial  palpi.  It  is  made  up  of  two  fleshy  lobes  or  leaves, 
bearing  on  the  outer  or  under  surface  many  fine,  transversal, 
subparallel  lines  or  ridges.  The  two  lobes  can  be  closed 
together  like  the  leaves  of  a  book. 

Make  a  drawing  showing  all  of  the  mouth-parts  from  the 
dorsal  view.  The  stylets  can  be  spread  apart  laterad,  so  as 
to  expose  the  under  ones. 

In  only  a  few  families  of  Diptera  are  free  mandibles  pres- 
ent, and  when  present  they  are  possessed,  as  already  men- 
tioned, only  by  the  females.  In  many  flies  there  are  no 
piercing  stylets,  and  as  representative  of  these  flies  without 
piercing  mouth-parts  the  common   house-fly  may  be  studied. 

MOUTH. PARTS    OF    THE    HOUSE-FLY. 

{Musca  domestica ;  order  Diptera^ 

In  the  house-fly  the  mandibular  and  maxillar  stylets  being 
gone,  we  find  only  the  trunk-like  labium,  with  the  labrum- 
epipharynx  lying  closely  appressed  to,  and  almost  fused  with 
its  dorsal  surface,  and  the  maxillary  palpi. 

•The  hypopharynx  and  the  epipharynx  (outgrowth  from  the  upper  wall  of 
the  pharyn.x)  are  in  most  insects  small,  fleshy,  and  inconspicuous. 


84 

The  maxillary  palpi  are  prominent,  but  are  only  one-seg- 
mented. The  labial  trunk  or  proboscis  may  be  described  as 
being  made  up  of  three  portions,  a  basal  third,  the  basipro- 
boscis,  from  which  arise  the  maxillary  palpi,  and  in  which  are 
imbedded  two  slender  chitinous  rods,  the  '■^maxillary  ten- 
dons" probably  representing  the  greatly  reduced  maxillae  ;  a 
middle  third,  the  mediproboscis,  strongly  chitinized  ;  and  a 
distal  third,  the  distiproboscis,  including  the  disk-like,  fleshy 
labella.  The  labella  is  like  that  of  the  horse-fly,  but  in  the 
house-fly  it  is  the  only  organ  for  obtaining  food.  With  it 
traversed  as  it  is  by  transverse,  horny,  chitinous  ridges,  the 
'■'■  pseudotrachea"  hard  food  substances  may  be  rasped  so  that 
fine  particles  of  food  mixed  with,  or  sometimes  dissolved  in, 
a  salivary  secretion,  which  issues  from  the  ridges,  can  flow 
into  the  mouth,  along  the  dorsal  furrow  of  the  labial  proboscis. 

Make  a  drawing  of  the  mouth-parts  from  a  lateral  view  ; 
and  also  of  a  portion  of  the  labella,  highly  magnified,  to 
show  disposition  of  the  pseudotrachese. 

MOUTH-PARTS    OF    THE    MONARCH    BUTTERFLY. 

[Anosia  plexippjis  ;  order  Lepidoptera.) 

In  the  higher  Lepidoptera  the  mouth-parts  have  under- 
gone a  profound  modification  ;  mandibles  are  wholly  want- 
ing and  the  labium  is  reduced  to  a  small,  immovable  sclerite, 
not  functional  in  food  getting.  The  maxillae,  on  the  other 
hand,  are  greatly  elongated  and  are  united  to  form  a  long, 
slender,  coiling,  sucking  tube. 

In  examining  the  mouth-parts  of  Anosia  it  will  be  found 
necessary  to  remove  carefully  the  scales  and  scale-hairs 
which  cover  the  head  before  bleaching. 

Labrum. — Immovably  joined  to  the  clypeus  is  a  very 
narrow,  mostly  transversal  sclerite,  the  labrum.  It  bears  two 
tapering,  cephalad.projecting  points,  the  pilifers,  rising  from 


85 

the  ends  of  the  transverse  portion  of  the  sclerite.  Each 
pilifer  bears  on  its  inner  margin  a  row  of  short  bristly  hairs, 
light  brown  in  color.  There  is  also  to  be  made  out  a  very 
small,  triangular  piece  projecting  cephalad  from  the  middle  of 
the  transverse  portion  of  the  labrum.     This  is  the  epipharymx. 

Mandibles. — The  vmndibles  are  wanting  in  Anosia.  (They 
are  present  in  an  aborted  condition  in  some  Lepidoptera  ; 
and  in  one  genus  of  small  moths,  Eriocephala,  are  present 
and  functional,  constituting,  with  the  maxillae  which  .are  not 
produced  into  a  sucking  tube,  true  biting  mouth-parts.) 

Maxillae. — The  long,  coiling,  sucking  tube  of  Anosia  (as 
of  all  the  Lepidoptera  possessing  functional  sucking  mouth- 
parts)  is  composed  of  the  greatly  extended,  opposed,  termi- 
nal portions  of  the  tnaxiilce.  In  addition,  there  is  a  fixed 
basal  part  of  each  maxilla,  which  cannot  be  divided  into 
cardo  and  stipes.  This  basal  part,  shining  brown,  extends 
caudad  and  ventrad,  partially  bounding  a  cavity  lying  be- 
tween it  and  the  labium.  The  sucking  tube  consists  of  two 
lateral  portions,  each  portion  representing  a  maxilla.  These 
parts  are  convex  outwardly  and  concave  inwardly.  By  the 
opposition  of  the  two  concave  aspects,  a  complete  central 
tube  is  formed.  The  maxillary  palpi  are  wanting  in  Anosia, 
and  in  most  of  the  butterflies,  although  present  in  a  one-  or 
two-  or  even  several-segmented  condition  among  most  of 
the  moths. 

Labium. — The  labium  is  a  fixed,  semi-membranous  sclerite, 
triangular  in  outline,  with  its  apex  projecting  cephalad  and 
joining  the  maxillar  proboscis  at  its  base.  The  labial  palpi 
are  large,  three-jointed,  and  covered  with  scales,  and  normally 
project  cephalo-dorsad.  They  are  inserted  on  tumid  spaces 
on  the  base  of  the  triangular  labium,  and  the  first  joint  is 
pedicellate. 

Make  a  drawing  of  the  cephalic  aspect  of  the  head  show- 
ing the  fixed  and  movable  parts. 


CHAPTER   VII. 

THE  VENATION  OF  THE  WINGS  OF   INSECTS.'* 
INTRODUCTION. 

In  form  an  insect's  wing  is  a  large,  membranous  append- 
age, which  is  thickened  along  certain  lines.  These  thick- 
ened lines  are  termed  the  veins  or  nerves  of  the  wing  ;  and 
their  arrangement  is  described  as  the  venation  or  neuration  of 
the  wings. 

It  has  been  found  that  the  venation  of  the  wings  of  closely 
allied  insects  is  very  similar,  and  that  great  differences  in 
this  respect  exist  between  insects  remotely  connected.  Hence, 
the  wings  afford  excellent  characters  for  use  in  the  classifica- 
tion of  insects.  In  fact,  as  slight  differences  in  venation  are 
easily  observed,  the  wings  being  spread  out  like  an  open 
page,  these  differences  are  probably  the  most  available  char- 
acteristics of  winged  insects  for  taxonomic  work.  It  is  im- 
portant, therefore,  that  the  student  of  entomology  should 
learn  early  in  his  course  the  more  important  facts  regarding 
this  subject. 

A  careful  study  of  the  wings  of  many  insects  has  shown 
that  the  fundamental  type  of  venation  is  the  same  in  all  of 
the  orders  of  winged  insects.     But  this  fact  is  evident  only 

'The  material  for  this  chapter  has  been  drawn  largely  from  an  essay  by  the 
writer,  entitled  Evolution  and  Taxonomy,  published  m  The  Wilder  Quarter-Cen- 
tury Book,  Ithaca,  1893,  and  from  a  series  of  articles  entitled  The  Wings  of  In- 
sects^ by  J.  H.  Comstock  and  j.  G.  Needham,  published  in  The  American 
Naturalist,  vol.  xxxii.  (1898),  and  vol.  xxxiii.  (1899). 

86 


87 

when  the  more  primitive  or  generalized  members  of  different 
orders  are  compared  with  each  other.  In  most  of  the  orders 
of  insects  the  greater  number  of  species  have  become  so 
modified  or  speciaUzed  as  regards  the  structure  of  their  wings 
that  it  is  difficult  at  first  to  trace  out  the  primitive  type. 

Note. — The  student  should  have  a  clear  idea  of  the  significance  of  the 
terms  generalized  and  specialized,  which  are  now  much  used  in  biology. 
Generalized  indicates  a  primitive  condition,  a  nearness  to  ancestral  forms. 
Thus,  the  most  generalized  member  of  a  group  (as  a  family  or  an  order)  is 
that  member  which  most  clearly  resembles  the  ancient  progenitor  of  that 
group.  Specialized,  on  the  other  hand,  indicates  remoteness  from  the 
primitive  type,  an  adaptation  to  more  special  conditions  of  existence.  Thus, 
the  most  specialized  member  of  a  group  is  the  one  that  departs  most  widely 
from  the  ancient  progenitor  of  that  group. 

These  terms  are  used  in  a  comparative  sense  ;  thus,  a  highly  specialized 
form  may  be  regarded  as  generalized  when  compared  with  forms  that  are 
still  more  highly  specialized. 

The  specimens  indicated  for  the  student  to  study  in  the 
following  part  of  this  course  have  been  selected  with  care  to 


Fig.  2. — Wing  of  Rhyphus. 

illustrate  gradually  increasing  degrees  of  divergence  from 
the  primitive  type.  In  the  case  of  each  order  studied,  the 
work  begins  with  a  comparatively  generalized  form,  and 
passes  step  by  step  to  those  that  are  more  specialized. 

The  flies  of  the  genus  Rhyphus  afford  good  examples  of 
comparatively  generalized  wings.  By  studying  a  wing  of 
one  of  these  flies  and  the  accompanying  figure  (Fig.  2)  the 


88 

student  can  gain  a  good  idea  of  the  type  of  the  wings  of  In- 
sects belonging  to  the  order  Diptera,  and  have  a  standard 
with  which  to  compare  wings  of  insects  of  other  orders. 
'  Longitudinal  veins  and  cross-veins. — The  veins  can 
be  grouped  under  two  heads  :  first, /(^//^////^////a/z;^^^,  those  that 
normally  extend  proximo  -  distad  ;  and  second,  cross-veins^ 
those  that  normally  extend  more  or  less  nearly  cephalo- 
caudad.  In  Figure  2,  three  of  the  cross-veins  are  indicated 
by  arrows,  near  the  middle  of  the  wing  ;  two  other  cross- 
veins  are  represented  near  the  the  base  of  the  wing,  but  are 
not  lettered.  All  other  veins  represented  in  this  figure  are 
longitudinal  veins. 

The  insertion  of  the  word  normally  in  the  above  definitions 
is  important ;  for  it  is  only  in  comparatively  generalized 
wings  that  the  direction  of  a  vein  can  be  depended  upon  for 
determining  to  which  of  these  two  classes  it  belongs.  A 
little  later  the  student  will  study  wings  in  which  the  direc- 
tion of  some  of  the  longitudinal  veins  has  been  so  modified 
in  the  course  of  specialization  that  they  extend  transversely 
{i.e.,  cephalo-caudad),  and  some  cross-veins  extend  in  a  longi- 
tudinal direction  {i.e.,  proximo-distad). 

Simple  veins  and  branched  veins. — Veins  are  either 
simple  or  branched.  The  veins  lettered  Sc  and  ist  A  in 
Figure  2  are  simple  veins  ;  between  these  there  are  three 
branched  veins. 

Jn  the  case  of  branched  veins  the  entire  vein,  including  all 
of  its  branches,  is  often  referred  to  as  a  single  vein.  Thus 
the  third  vein  in  the  wing  of  Rhyphus,  counting  the  thick- 
ened, cephalic  margin  of  the  wing  as  the  first  vein,  is  termed 
the  radius  or  vein  R ;  and  by  this  expression  we  include 
both  the  main  stem  of  the  vein  and  its  three  divisions.  On 
the  other  hand,  each  division  of  a  branched  vein  is  often 
termed  a  vein.  Thus  the  first  division  of  the  radius,  count- 
ing from  the  cephalic  margin  of  the  wing,  is  termed  radius- 


89 

one  or  vein  R^,  and   the  second   division,   radius-two  or  vein 
Ji^,  and  so  on  till  all  are  numbered. 

Note. — In  the  most  generalized  flies  known  to  us,  the  radius  is  five- 
branched.  But  in  most  flies  some  of  the  branches  of  this  vein  coalesce  so 
that  the  number  of  apparent  branches  is  less  than  five.  In  Rhyplms  veins 
R-i  and  R^  coalesce  so  as  to  appear  as  a  single  vein.  In  order  to  indicate 
that  this  apparently  simple  vein  is  composed  of  two  veins,  and  in  order  thai 
homologous  veins  in  different  insects  shall  bear  the  same  designation,  this 
compound  vein  is  termed  radius-two-plus-three  or  vein  R^  +  3.  In  the  same 
way,  what  appears  to  be  the  third  branch  of  the  radius  in  Rhyphits  is  really 
the  fourth  and  fifth  coalesced,  and  is,  therefore,  designated  as  radius-four- 
plus-five  or  vein  R^  +  5.  The  tracing,  out  of  the  homologies  of  the  branches 
of  veins  is  often  very  difficult ;  but  it  is  of  the  greatest  importance  in  deter- 
mining the  relationships  of  different  genera  or  of  families. 

Names  of  the  longitudinal  wing-veins. — There  have 
been  many  different  sets  of  names  applied  to  the  veins  of 
wings.  Not  only  have  the  students  of  each  order  of  insects 
had  a  peculiar  nomenclature,  but  in  many  cases  different 
writers  on  the  same  order  have  used  different  sets  of  terms. 
This  condition  of  affairs  was  incident  to  the  beginning  of  the 
science,  the  period  before  the  correspondence  of  the  veins  in 
the  different  orders  had  been  worked  out.  But  now  the  time 
has  come  when  it  is  practicable  to  apply  a  uniform  nomencla- 
ture to  the  longitudinal  wing-veins  of  all  orders  ;  and  the 
following  set  of  terms  has  been  proposed  for  that  purpose  : 

Costa. — The  vein  extending  along  the  cephalic  or  costal 
margin  of  the  wing  is  the  casta. 

Subcosta. — Immediately  caudad  of  the  costa  and  extending 
parallel  with  it,  is  a  vein,  which  is  usually  simple  in  flies  ;  this 
is  the  subcosta  (Fig.  2,  Sc). 

Radius. — Immediately  caudad  of  the  subcosta  there  is  a 
vein  which  in  generalized  insects  is  always  branched  ;  this  is 
the  radius.  In  Rhyphus,  the  radius  is  three-branched  (Fig.  2, 
R,,  R,  +  3,  and  R,  +  ,). 


90 

Media. — Traversing  the  middle  of  the  wing  there  is  a 
longitudinal  vein  which  is  always  branched  in  generalized 
insects  ;  this  is  the  media.  In  Rhyphus  the  media  is  three- 
branched  (Fig.  2,  J/,,  J/„  and  M^. 

Cubitus. — The  third  and  last  of  the  branched  veins  in  flies 
is  the  cubitus.  This  vein  is  two-branched  in  Rhyphus  (Fig. 
2,  CWj  and  Cu^. 

Anal  veins. — Caudad  of  the  cubitus  there  is  in  Rhyphus  Si 
single  well-developed  vein  ;  this  is  termed  an  anal  vein.  As 
in  more  generalized  insects  there  are  three  anal  veins,  and  as 
this  is  believed  to  be  the  first  of  the  series,  it  is  designated 
Xht  first  anal  vein  (Fig.  2,  1st  A).  A  rudiment  of  the  second 
anal  vein  persists  in  Rhyphus  j  this  is  indicated  in  the  figure 
by  a  dotted  line,  at  the  left  of  the  letter  A. 

Designation  of  the  longitudinal  wing-veins  by  numbers.— Several 

writers  have  designated  the  longitudinal  wing-veins  by  numbers.  In  Com- 
stock's  Manual  for  the  Study  of  Insects  both  the  names  given  above  and 
numbers  are  used.  The  following  table  indicates  the  correspondence  of  the 
names  and  numbers ;  and  Figure  3  represents  the  wing  of  a  butterfly,  with 
the  veins  and  cells  numbered  according  to  the  system  used  in  that  manual. 

Costa  =  vein  I.  Cubitus  =  vein  VII. 

Subcosta  =  vein  II.  1st  anal  vein  =  vein  VIII.* 

Radius  =  vein  III.  2d  anal  vein  =  vein  IX. 

Media  =  vein  V.  3^  anal  vein  =  vein  X. 

It  will  be  observed  that  in  the  above  table  the  numbers  IV  and  VI  are 
omitted.  At  the  time  the  Manual  for  the  Study  of  Insects  was  published,  it 
was  believed  that  two  other  longitudinal  veins  (the  so-called /;rw^^m  and 
postmedia)  were  present  in  certain  orders  of  insects,  and  the  numbers  IV 
and  VI  were  applied  to  these  veins.  It  has  since  been  determined  that  this 
conclusion  was  based  on  an  error. 

Certain  writers  number  the  wing  veins  without  omitting  the  numbers  IV 
and  VI,  designating  the  media  as  vein  IV  and  the  cubitus  as  vein  V. 

•  As  the  anal  furrow,  which  is  described  later,  was  supposed  to  represent  the 
first  anal  vein,  it  is  numbered  VIII  in  the  descriptions  of  wings  of  Diptera  and 
Hymenoptera  in  the  work  cited,  and  the  true  first  anal  vein  is  numbered  IX. 


91 

There  are  still  other  writers  who  do  not  regard  the  costa  as  a  true  vein, 
and,  therefore,  designate  the  subcosta  as  vein  I. 

The  result  is  that  there  are  three  distinct  systems  of  numbering  the  wing- 
veins,  in  addition  to  several  old  systems  which  were  applied  to  single  orders. 
It  seems  better,  therefore,  to  designate  the  wing-veins  by  names,  and  use 
abbreviations  of  these  names  in  lettering  figures. 

Names  of  the  cross-veins. — In  the  Diptera  and  in  cer- 
tain other  orders  of  insects  there  are  so  few  cross-veins  that 
it  is  practicable  to  apply  names  to  them  ;  these  are  as  follows  : 

The  humeral  c7'oss-vein. — This  is  a  single  cross-vein  ex- 
tending from  the  subcosta  to  the  costa  near  the  base  of  the 


Fig.  3. — Fore  wing  of  a  butterfly  with  the  veins  and  cells  numbered. 

wing.  This  is  the  most  constant  of  all  of  the  cross-veins. 
It  is  represented  in  Figure  2,  but  is  not  lettered. 

77/1?  radial  cross-vein. — This  is  a  cross- vein  which  divides 
cell  R^.  (The  cells  are  defined  a  little  later.)  The  radial 
cross-vein  is  not  represented  in  Figure  2. 

The  radio-medial  cross-vein. — This  is  a  cross-vein  extending 
from  the  radius  to  the  media,  usually  near  the  center  of  the 
wing,  and  is  designated  by  the  abbreviation  r-m.  When  in 
its  typical  position  this  cross-vein  extends  from  vein  R^j^^  to 
vein  J/,4.2  ;  this  results  in  one  end  being  opposite  cell  R^  and 
the  other  end  opposite  cell  1st  M^. 


*+Ar-* 


92 

The  medio-cubital  cross-vein. — This  is  a  cross-vein  extending 
from  the  media  to  the  cubitus,  usually  near  the  center  of  the 
wing.  It  is  designated  by  the  abbreviation  vi-cu.  When  in 
its  typical  position  this  cross-vein  extends  from  a  point  near 
the  base  of  vein  M^^,^  to  a  point  near  the  base  of  vein  Cu^. 

The  medial  cross-vein. — This  is  a  cross-vein  extending 
from  vein  M^  to  vein  M^  ;  it  is  designated  by  the  abbrevia- 
tion in.  The  presence  or  absence  of  this  cross-vein  is  often 
a  character  of  considerable  taxonomic  importance. 

The  arculus. — In  many  insects  there  is  what  appears  to  be 
a  cross-vein  extending  from  the  radius  to  the  cubitus  near 
the  base  of  the  wing.     This  has  been  termed  the  arculus  by 

writers  on  the 
Odonata,  and  the 
use  of  this  term 
has  been  extended 

FIG.  4.-The  arculus,  diagrammatic.  ^^      ^„      ^^^^^^      j^ 

which  there  is  a  similar  arrangement  of  the  veins  in  this  part 
of  the  wing.  The  arculus  is  designated  by  the  abbreviation 
ar.  Usually  when  the  arculus  is  present  the  media  appears 
to  arise  from  it.  The  fact  is,  the  arculus  is  compound,  being 
composed  of  a  section  of  the  media  and  a  cross-vein.  The 
structure  of  this  part  can  be  clearly  seen  in  the  Odonata 
(Fig.  4).  In  Ryphus  (Fig.  2)  the  arculus  appears  as  a  simple 
cross-vein  extending  from  the  radius  to  the  cubitus,  and  a 
part  of  the  base  of  the  media  is  atrophied. 

Designation  of  the  cells  of  the  wing.— The  thin  spaces 
of  the  wings  which  are  bounded  by  the  veins  are  called  cells. 
In  descriptions  of  wings  it  is  often  desirable  to  refer  to  one 
or  more  of  the  cells.  It  is  necessary,  therefore,  to  have  a 
nomenclature  of  the  cells  of  the  wing,  as  well  as  of  the  wing- 
veins. 

Having  named  the  wing-veins,  the  simplest  possible 
method  of  designating  the  cells  of  the  wing  is  to  apply  to 


93 

each  the  abbreviation  of  the  name  of  the  vein  that  forms  its 
cephalic  (front)  margin.  It  should  be  borne  in  mind,  how- 
ever, that  by  modifications  of  the  typical  arrangement  of  the 
wing-veins,  a  vein  that  normally  forms  the  cephalic  margin 
of  a  cell  may  apparently  bear  a  very  different  relation  to  it  ; 
and  this  must  be  taken  into  account  if  we  are  to  apply  the 
same  term  to  homologous  cells  throughout  the  insect  series. 

The  cells  of  the  wing  fall  naturally  into  two  groups  :  first, 
those  on  the  basal  part  of  the  wing ;  and  second,  those 
nearer  the  distal  end  of  the  wing.  The  former  are  bounded 
by  the  principal  veins  ;  the  latter,  by  the  branches  of  the 
forked  veins  ;  a  corresponding  distinction  is  made  in  desig- 
nating the  cells.  Thus  the  cell  lying  behind  the  main  stem 
of  the  radius  and  on  the  basal  part  of  the  wing  is  designated 
as  cell  R ;  while  the  cell  lying  behind  the  radius-one  is 
designated  as  cell  R^. 

It  should  be  remembered  that  the  coalescence  of  two 
veins  results  in  the  obliteration  of  the  cell  that  was  between 
them.  Thus  when  veins  R^  and  R^  coalesce,  as  in  Rhyphus 
(Fig.  2),  the  cell  lying  behind  R,^^  is  cell  R^,  and  not  cell 
R^+y  cell  R^  having  been  obliterated. 

When  one  of  these  principal  cells  is  divided  into  two  or 
more  parts  by  one  or  more  cross-veins,  the  parts  may  be 
numbered,  beginning  with  the  proximal  one.  Thus  in  Rhy- 
phus (Fig  2)  cell  M^  is  divided  by  the  medial  cross-vein  into 
two  parts,  which  are  designated  as  cell  ist  M^  and  cell  2d  M^ 
respectively. 

The  application  of  this  system  of  naming  the  cells  of  the 
wing  is  an  easy  matter  in  those  orders  where  the  wings  have 
few  veins  ;  but  in  those  orders  where  many  secondary  veins 
are  developed  it  is  more  difficult  of  application.  In  the  lat- 
ter case  we  have  to  do  with  areas  of  the  wing  rather  than 
with  separate  cells.  Thus,  for  example,  it  will  be  seen  later 
that  in  certain  Neuroptera  the  area  R^  is  divided  by  several 


94 

longitudinal  veins,  which  are  connected  by  many  cross- veins, 
the  area  J^^  (which  is  strictly  homologous  with  cell  -/?J  being 
composed  of  a  large  number  of  secondary  cells. 

The  furrows  of  the  wing.— The  wings  of  comparatively 
few  insects  present  a  flat  surface  ;  in  most  cases  we  find  that 
the  membrane  is  thrown  into  a  series  of  folds  or  corruga- 
tions. This  corrugating  of  the  wing  in  some  cases  adds 
greatly  to  its  strength.  This  is  well  shown  by  the  wings  of 
dragon  flies  ;  and  in  most  orders  the  costal  margin  of  the 
wing  is  strengthened  by  a  fold  between  the  costa  and  the 
radius,  the  subcostal  fold.  In  other  cases,  the  corrugations 
are  the  result  of  a  folding  of  the  wing  when  not  in  use  ;  this 
is  well  shown  in  the  anal  area  when  this  part  is  broadly  ex- 
panded. 

It  rarely  happens  that  there  is  occasion  to  refer  to  indi- 
vidual members  of  either  of  these  classes  of  folds,  except, 
perhaps,  to  the  one  that  has  just  been  designated  as  the  sub- 
costal fold.  But  there  are  three  other  furrows  which  it  is 
necessary  to  designate,  as  they  are  frequently  referred  to. 
These  are  the  anal  furrow,  the  median  furrow,  and  the 
nodal  furrow.  Only  the  first  of  these  is  well-marked  in 
the  Diptera  ;  but  for  sake  of  completeness  all  are  defined 
here. 

The  a?ial  furrow. — This  is  a  longitudinal  furrow  which  is 
usually  between  the  cubitus  and  the  first  anal  vein.  In  the 
figure  of  the  wing  of  Rhyphus  (Fig,  2),  it  is  represented  by 
a  dotted  line  immediately  behind  the  cubitus.  In  the  order 
Diptera  it  is  always  in  this  position  if  present. 

The  median  furrow. — This  is  a  longitudinal  furrow  which 
is  usually  between  the  radius  and  the  media.  It  is  well 
marked  in  many  of  the  Hemiptera,  where  it  separates  the 
embolium  from  the  remainder  of  the  corium  ;  and  in  the 
Hymenoptera  its  course  is  marked  by  a  series  of  weak  spots 
(bullae)  in  certain  veins. 


95 

The  nodal  furrow. — This  is  a  transverse  suture  beginning 
at  a  point  in  the  costal  margin  of  the  wing,  corresponding 
to  the  nodus  of  the  Odonata,  and  extending  towards  the 
inner  margin  of  the  wing.  It  crosses  a  varying  number  of 
veins  in  different  orders  of  insects. 

The  furrows  of  the  wing  are  in  no  sense  homologous  or  even  analogous 
to  veins.  More  than  this,  the  relative  positions  of  the  furrows  and  of  the 
wing-veins  are  not  constant ;  for  it  frequently  happens  that  the  course  of  a 
vein  has  been  so  modified  that  it  crosses  the  line  of  a  furrow  and  the  rel- 
ative positions  of  the  two  are  thus  reversed.  If  this  fact  had  been  under- 
stood by  Adolph  we  would  have  been  spared  his  misleading  theory  of  alter- 
nating concave  and  convex  veins.  * 

Margins  of  wings. — An  insect's  wing  is  more  or  less 
triangular  in  outline  ;  it,  therefore,  presents  three  margins  ; 
the  costal  tnargin  (Fig.  3,  a-b)  ;  the  outer  margin  (Fig.  3,  b-c), 
and  the  inner  margin  (Fig.  3,  c-d). 

Angles  of  wings. — The  angle  at  the  base  of  the  costal 
margin  (Fig.  3,  a)  is  the  humeral  angle  j  that  between  the  cos- 
tal margin  and  the  outer  margin  (Fig.  3,  b)  is  the  apex  of 
the  wing  J  and  the  angle  between  the  outer  margin  and  the 
inner  margin  (Fig.  3,  c)  is  the  anal  angle. 

The  typical  branching  of  the  wing-veins.— In  order 
to  determine  the  homologies  of  the  branches  of  a  forked 
vein  when  some  of  the  cells  have  been  obliterated  by  the 
coalescence  of  branches,  it  is  necessary  to  know  what  was 
the  primitive  type  of  branching  of  this  vein.  For  this  rea- 
son an  effort  has  been  made  to  determine  the  probable 
structure  of  the  wing  of  the  primitive  winged  insect. 

In  the  study  of  the  development  of  wings,  it  has  been 
found  that  in  the  more  generalized  insects  the  cavities  of 
the  longitudinal  wing-veins  are  formed  about  tracheae,  and 

"  G.  Ernst  Adolph,  Ueber  Insectenflugel.  /\/ova  Acta  der  ksl.  Leop.-Carol- 
Deutschen  Akademie  der  Natur/orscher,  Bd.  xli,  pp.  215-251.     1879. 


96 

that  these  trachese  exhibit  a  striking  similarity  in  their  origin 
and  mode  of  branching  in  the  nymphs  and  pupae  of  the 
more  generalized  members  of  most  of  the  orders  of  insects. 
We  have  been  able,  therefore,  to  present  a  hypothetical  type, 
which  we  believe  represents  approximately  what  was  the 
arrangement  of  the  tracheae  in  the  nymph  of  the  primitive 
winged  insect  (Fig.  5),  and,  as  the  wing-veins  of  the  adult 
are  developed  about  the  tracheae  of  the  wing  of  the  nymph, 


jdA 


id  A 


Fig.  5.— Diagram  representing  the  hypothetical  arrangement  of  the  tracheae  in 
a  wing  of  a  nymph  of  the  primitive  winged  insect. 


the  same  figure  will  serve  to  indicate  the  probable  mode  of 
branching  of  the  wing-veins  in  the  adult  of  the  primitive 
winged  insect. 

The  radial  sector. — When  the  radius  preserves  its  prim- 
itive mode  of  branching,  it  separates  at  its  first  fork  into 
two  unequal  parts  ;  the  first  of  these  is  vein  R^  ;  the  other 
gives  rise  to  the  remaining  four  branches  of  the  radius  (Fig, 
5).  This  second  part  of  the  radius,  including  its  branches, 
is  termed  the  radial  sector  or  vein  Hg, 


97 


IDENTIFICATION    OF    THE    WING-VEINS    AND    OF    THE    CELLS   OF 
THE    WING    IN    DIPTERA. 

As  the  chief  object  of  the  followhig  work  is  to  give  the 
student  training  in  tracing  the  homologies  of  wing-veins, 
comparatively  little  information  will  be  given  directly.  The 
student  will  be  furnished  in  each  case  with  the  wing  to  be 
studied,  and  his  studies  should  take  the  following  course  : — 

Directions  for  the  study  of  wings. — Make  a  drawing 
of  the  wing,  based  upon  a  careful  study  of  it  with  a  com- 
pound microscope,  using  a  low  power.  The  drawing  should 
be  first  made  with  a  pencil  ;  after  it  has  been  criticised  by 
the  teacher,  the  lines  should  be  inked ;  ink  the  lines  repre- 
senting the  media  with  red  ink,  use  black  ink  for  the  re- 
mainder of  the  wing,  including  the  medial  cross  vein.  Make 
the  drawing  on  a  sufificiently  large  scale  so  that  each  vein 
can  be  represented  distinctly  ;  in  most  cases  the  drawings 
should  be  somewhat  larger  than  Figure  3. 

Number  each  vein  and  cell  of  the  wing. 

Note  the  more  important  features  of  its  venation,  and 
especially  the  more  important  departures  from  the  primitive 
type  of  the  order  as  indicated  by  the  generalized  form  first 
studied.  In  the  Diptera  the  wing  of  Rhyphus  (Fig.  2)  may 
be  used  as  a  generalized  type,  although  in  certain  respects 
other  wings  will  be  found  to  be  more  generalized. 

The  following  are  some  of  the  more  important  points  to  be 
noted  :  Whether  the  subcosta  is  simple  or  forked  at  the  tip  ; 
the  number  of  the  branches  of  the  radius  ;  in  this  connection 
determine  which  of  the  radial  cells  has  been  obliterated  by 
the  coalescence  of  branches  of  the  radius  (study  Fig.  5)  ;  the 
position  of  the  radio-medial  cross-vein  ;  the  number  of  the 
branches  of  the  media  (in  none  of  the  common  Diptera  has 
the  media  more  than  three  branches  ;  and  the  mode  of  dis- 
appearance of  vein  M^  in  this  order  has  not  been  determined 


98 

as  yet.  For  this  reason  the  student  need  not  take  this  vein 
into  consideration  in  his  studies  of  dipterous  wings)  ;  the 
division  or  not  of  cell  M^  ;  the  presence  or  absence  of  cell 
M^ ;  the  courses  of  the  branches  of  the  cubitus  ;  the  extent 
of  the  anal  furrow ;  and  the  course  of  the  anal  vein. 

Wing  of  a  Tabanid. — A  specimen  of  one  of  the  horse- 
flies, Tabanus,  will  be  given  the  student  for  examination. 
Observe  iht  subcostal  fold,  and  note  that  this  corrugation  stiff- 
ens the  wing. 

Make  a  drawing  of  a  mounted  Tabanid  wing,  which  will 
be  furnished  on  application  to  the  instructor.  Note  that  in 
the  mounted  wing  the  subcosta  is  more  or  less  concealed  by 
the  radius,  although  the  two  veins  are  distinct,  as  was  seen 
in  the  unmounted  specimen.  Represent  these  two  veins  as 
slightly  separated  in  your  drawing. 

In  the  description  of  this  wing,  state  in  what  respect  it  is 
more  generalized  than  that  of  Rhyphus,  and  in  what  respect 
it  is  more  specialized. 

Wing  of  an  Asilid. — A  wing  of  a  robber-fly  of  the  genus 
Erax  will  be  used  as  an  example.  Note  a  method  of  coa- 
lescence of  veins  not  exhibited  by  Rhyphus. 

Wing  of  a  Bombyliid. — The  example  used  is  a  wing  of 
Pantarbes,  one  of  the  bee-flies. 

Wing  of  a  Scenopinid. — The  wing  used  is  that  of  a  com- 
mon window-fly,  Scenopinus. 

Wing  of  an  Empidid. — The  wing  used  is  that  of  Rhani- 
phofnyia,  one  of  the  dance-flies. 

Wing  of  a  Muscid. — The  wing  used  is  that  of  the  com- 
mon house-fly,  Miisca  domestica. 

Wings  of  Dilichopodids.— The  wings  of  two  of  the 
long-legged  flies  will  be  used.  The  first  belongs  to  the  genus 
Psilopiis;    the  second  to  the  genus  Dolichopus. 

Wing  of  a  Syrphid. — The  wings  of  a  fly  of  the  genus 
Syrphus   will    be    used.     Note    the    vein-like    structure    be- 


99 

tween  the  radius  and  the  media  ;  this  is  termed  the  spurious 
vein. 

Wing  of  Culex. — The  wing  of  a  mosquito  is  used  as  an 
example  of  the  venation  of  the  midge-Hke  flies.  In  these 
the  number  of  the  branches  of  the  radial  sector  is  reduced  in 
away  different  from  that  seen  in  the  families  previously  stud- 
ied. Compare  with  the  Asilid,  the  Bombyliid,  and  the  Sceno- 
pinid. 

THE    WINGS   OF    LEPIDOPTERA. 

As  the  wings  of  Lepidoptera  are  covered  with  scales,  it  is 
difficult  to  determine  the  nature  of  their  venation  without 
specially  preparing  them  for  this  purpose.  After  a  student 
has  become  familiar  with  the  type  of  venation  characteristic 
of  the  order,  he  can  usually  determine  the  course  of  any 
particular  vein  by  putting  a  drop  of  chloroform  on  the  part 
of  the  wing  to  be  examined  ;  this  will  render  the  veins  more 
distinct  for  a  few  seconds.  Or  the  scales  can  be  removed 
from  a  small  part  of  the  wing  with  a  small  artist's  sable 
brush.  But  when  a  very  careful  study  of  the  venation  of  a 
wing  is  to  be  made,  it  should  be  bleached  and  mounted  on  a 
card  or  on  a  glass  slip,  in  order  that  it  may  be  studied  with 
a  compound  microscope.  The  following  is  the  method  of 
bleaching  wings  :  — 

1.  Remove  the  wings  carefully  so  as  not  to  break  the  fren- 
ulum if  there  be  one  ;*  it  is  well  to  remove  the  patagium 
first. t 

2.  Dip  the  wings  in  alcohol  in  order  to  wet  them. 

3.  Immerse  them  for  an  instant  in  hydrochloric  acid  (muri- 
atic acid).  Use  for  this  purpose  dilute  acid,  one  part  acid  to 
nine  parts  water. 

*  The  frenulum  is  a  strong  spine  or  bunch  of  bristles  borne  by  the  hind  wing 
at  the  humeral  angle  in  most  moths. 

t  The  patagia  are  scale-like  appendages  at  the  bases  of  the  fore  wings. 


lOO 

4.  Put  them  in  Labaraque  solution  with  the  upper  surface 
of  the  wings  down,  and  leave  them  there  till  the  color  has 
been  removed  from  the  scales.  If  a  wing  bleaches  slowly, 
the  process  can  be  hastened  by  dipping  it  in  the,  dilute  acid 
and  returning  it  to  the  Labaraque  solution  from  time  to  time. 
This  solution  can  be  procured  of  most  druggists.  It  deteri- 
orates if  left  exposed  in  strong  sunlight.  If  it  cannot  be  ob- 
tained use  an  aqueous  solution  of  chloride  of  lime. 

5.  When  a  wing  is  bleached,  put  it  in  alcohol  and  leave  it 
there  till  after  it  floats.  This  is  to  wash  off  the  Labaraque 
solution.  The  wing  can  then  be  mounted  on  a  card.  But  it 
is  better  to  mount  it  as  described  below. 

6.  Transfer  the  wing  to  a  clearing  mixture,  if  it  is  to  be 
mounted  in  balsam,  and  leave  it  there  five  or  ten  minutes. 
This  is  to  remove  any  water  there  may  be  on  it.  A  good 
clearing  mixture  can  be  made  by  mixing  two  parts  by  measure 
of  carbolic  acid  crystals  and  three  parts  of  rectified  oil  of 
turpentine- 

7.  Put  the  wing  on  a  glass  slip  with  considerable  clearing 
mixture  under  it  to  avoid  bubbles  ;  put  Canada  balsam  on 
top,  and  cover  with  a  cover  glass.  In  the  case  of  small  wings, 
it  is  best  to  transfer  them  from  one  solution  to  another,  and 
to  the  glass  slip  by  means  of  a  camel 's-hair  brush.* 

Wings  bleached  and  mounted  in  this  way  make  an  im- 
portant addition  to  a  collection.  The  slides  should  be  care- 
fully labelled  ;  and  the  insect  from  which  the  wings  were 
taken  should  be  kept  with  the  slide.  It  is  our  practice  to  re- 
move always  the  wings  from  the  right  side,  and  then  to  mount 
the  slide  in  the  collection  at  the  right  of  the  insect  from 
which  the  wings  were  taken.  Uniformity  in  this  respect  adds 
greatly  to  the  appearance  of  the  collection. 


'  In  the  case  of  very  small  wings,  as  those  of  Tineids,  the  very  fine  veins  are 
more  distinct  when  mounted  in  glycerine-jelly  than  when  mounted  in  Canada 
balsam. 


lOI 

Wings  of  Hepialus. — Mounted  specimens  of  the  two 
wings  of  one  side  of  a  moth  belonging  to  the  genus  Hepialus 
will  be  furnished  the  student  for  study.  Be  very  careful  of 
the  specimens,  as  moths  of  this  genus  are  rare  in  this 
country. 

The  membranous  lobe  near  the  base  of  the  inner  margin 
of  the  fore  wing  is  th&Jugum.  This  extends  under  the  costal 
margin  of  the  hind  wing,  while  the  greater  part  of  the  inner 
margin  of  the  fore  wing  overlaps  the  hind  wing.  This  ar- 
rangement assures  the  acting  together  of  the  two  wings. 

Wings  of  a  Cossid. — Mounted  wings  of  one  of  the 
Cossidte  will  be  furnished  the  student  for  study. 

Wings  of  the  monarch  butterfly. — The  student  will 
be  furnished  with  specimens  of  the  two  wings  of  one  side  of 
the  monarch  butterfly,  Anosia  plexippus. 

Study  the  fore  wing  first.  Explain  the  significance  of  the 
three  short  spurs  that  project  into  the  distal  end  of  the  large 
cell  near  the  middle  of  the  wing. 

Wings  of  frenate  moths. — Specimens  of  moths  be- 
longing to  the  family  NoctuidcK  will  be  used  as  illustrations  of 
Lepidoptera  in  which  the  frenulum  is  well  developed.  Two 
specimens,  a  male  and  a  female  of  the  same  species,  should  be 
studied  if  practicable. 

Remove  the  wings  of  the  right  side  of  the  female,  and 
bleach  and  mount  them. 

Figure  these  wings. 

Remove  the  wings  of  the  right  side  of  the  male,  and  bleach 
and  mount  them. 

Figure  these  wings. 

Describe  the  secondary  sexual  distinction  exhibited  by  the 
wings  of  this  species. 

How  could  one  of  these  types  have  been  derived  from  the 
other  ? 

Study  the  wings  of  the  male  that  have  not  been  bleached, 


102 

and  note  the  fretudum  hook  on  the  fore  wing,  which  receives 
the  tip  of  the  frenulum.  It  may  be  necessary  to  remove 
some  of  the  hairs  from  the  base  of  the  wing.  Use  a  small 
sable  brush  for  this. 

Study  the  unbleached  wings  of  the  female,  and  note  the 
absence  of  a  frenulum  hook. 

Compare  the  hind  wing  of  the  monarch  butterfly  with  the 
hind  wings  of  these  moths,  and  discuss  the  differences  be- 
tween them. 

THE    WINGS    OF    HYMENOPTERA. 

The  determination  of  the  homologies  of  the  wing-veins  of 
Hymenoptera  is  very  difficult  ;  as  even  in  the  most  general- 

^^  f  f 


jdA 


2iA 


Fig.  6.  — The  veins  of  a  typical  hymenopterous  wing. 

ized  of  the  living  members  of  the  order,  the  venation  of  the 
wings  departs  widely  from  the  primitive  type.  For  this 
reason  no  student  should  begin  his  study  of  the  venation  of 
wings  with  hymenopterous  insects.  In  the  following  dis- 
cussion it  will  be  assumed  that  the  student  has  carefully  per- 
formed the  work  on  the  wings  of  Diptera  outlined  in  the 
preceding  pages  ;  and  the  first  step  for  him  to  take  at  this 
point  m  his  studies  is  to  take  his  drawings  of  dipterous 
wings  and  review  that  work. 


I03 

The  method  of  specialization  of  wing-veins  which  has 
taken  place  in  the  Hymenoptera  can  be  most  easily  seen  by 
a  study  of  the  fore  wings  of  certain  sawflies.  The  most  use- 
ful for  this  purpose  that  we  have  found  belong  to  the  genera 
Patnphilius  and  Macroxyela.  If  we  are  right  in  our  interpre- 
tation of  the  wings  of  these  insects,  there  is  preserved  in 
each  genus  all  of  the  primitive  wing-veins  with  a  single  ex- 
ception. And,  as  in  each  of  these  genera  a  different  vein  is 
lost,  we  are  able  to  make  a  figure  of  a  typical  wing  from  a 


Fig.  7. — The  cells  of  a  typical  hymenopterous  wing." 

study  of  the  two  genera.  Figures  6  and  7  represent  such  a 
wing  ;  in  the  former  the  veins  are  lettered  ;  in  the  latter,  the 
cells.f 

In  the  wings  of  these  sawflies  the  anal  furrow  and  the 
median  furrow  are  both  well  marked,  and  are  in  the  typical 
positions  ;  that  is,  the  anal  furrow  is  immediately  in  front  of 
the  first  anal  vein,  and  the  median  furrow  is  in   front  of  the 


*  The  cell  lettered  5  is  probably  Sci.  When  it  is  thickened  and  opaque,  as 
is  frequently  the  case  in  this  order,  it  is  termed  the  stigma. 

t  Figures  6  and  7  represent  the  venation  of  the  fore  wing  o{ Pamphilius^  except 
that  vein  R„,  which  is  lacking  in  this  genus,  is  added.  This  vein  is  well  pre- 
served in  Macroxyela,  but  in  Macroxyela  vein  Cu.^  is  lost.  See  Comstock, 
Manual  for  the  Study  0/  Insects,  p.  606,  for  figures  of  the  wings  of  these  two 
genera. 


104' 

media.  The  furrows  are  represented  by  dotted  lines  in  the 
figures. 

In  the  anal  area  {i.e.,  that  portion  of  the  wing  back  of  the 
anal  furrow)  the  three  typical  veins  are  preserved  ;  but  they 
coalesce  to  a  considerable  extent,  both  at  the  base  and  near 
the  margin  of  the  wing. 

In  the  basal  part  of  the  pre-anal  area  [i.e.,  that  portion  of 
the  wing  in  front  of  the  anal  furrow)  the  stems  of  the  princi- 
pal veins  are  as  follows  :  the  costa  coincides  with  the  costal 
margin  of  the  wing  (Fig.  6,  C)  ;  the  subcosta  (Sc)  is  well  pre- 
served and  is  forked  ;  back  of  the  subcosta  is  a  strong  stem 
formed  by  the  coalescence  of  the  other  three  veins  ;  the 
cubitus  (Cu)  soon  separates  from  the  stem,  extending  in  a 
curve  towards  the  anal  furrow  ;  while  the  radius  and  the 
media  coalesce  for  about  half  their  length.  In  order  to 
make  these  veins  more  distinct  in  the  figure  we  have  marked 
the  free  portion  of  the  media  with  cross  lines. 

When  we  pass  from  the  consideration  of  the  main  stems  to 
a  study  of  the  branches,  we  meet  a  much  more  complicated 
problem,  a  problem  which  could  not  have  been  solved  by  a 
study  of  Hymenoptera  alone.  But  a  knowledge  of  the  meth- 
ods of  specialization  of  the  wings  of  Diptera  gives  a  key  to  an 
understanding  of  the  wings  of  Hymenoptera. 

We  will  study  first  the  branches  of  the  cubitus.  Spread 
out  before  you  your  drawings  of  the  wings  of  the  following 
insects,  and  arrange  them  in  the  order  named  :  a  Bombyliid, 
a  Scenopinid,  and  an  Empidid.  Now  study  the  figure  of  a 
wing  of  Rhyphiis  (Fig.  2,  p.  87)  and  note  that  while  in  Rhyphus 
veins  Cu^  and  ist  A  retain  their  primitive  position,  in  the 
three  wings  named  above  these  two  veins  exhibit  varying  de- 
grees of  coalescence. 

A  similar  method  of  specialization  has  taken  place  in  the 
Hymenoptera,  but  in  this  order  both  branches  of  the  cubitus 
coalesce  with  the  first  anal  vein  ;  and  this  coalescence  has 


105 

proceeded  so  far  that  both  branches  cross  the  anal  furrow 
and  end  in  the  anal  vein  remote  from  the  margin  of  the  wing. 
(See  Fig.  6.) 

It  should  be  noted  that  vein  Cu^  is  rarely  preserved  in  this 
order,  even  in  the  more  generalized  forms.  We  have  found 
it  only  in  the  genus  Paniphilius.  In  Macroxyela^  the  posi- 
tion of  the  fork  of  the  cubitus  is  indicated  by  a  bend  in  this 
vein. 

If  the  branches  of  the  media  be  now  examined,  it  will  be 
seen  that  vein  J/,  (Fig.  6)  extends  longitudinally  near  the 
centre  of  the  distal  part  of  the  wing,  its  primitive  course 
being  modified  slightly  if  at  all.  Vein  M^  follows  a  course 
similar  to  the  course  of  this  vein  in  the  Bombyliid  ;  so  also 
does  the  medial  cross-vein  (Fig.  6,  ;//).  A  comparison  of 
the  position  of  cells  J/,,  ist  M^,  and  2d  M^  in  the  Bombyliid 
and  in  the  typical  hymenopterous  wing  (Fig.  7)  is  very  in- 
structive. 

Returning  to  Paniphilius  (Fig.  6),  we  see  that  vein  M^ 
coalesces  with  the  first  anal  vein,  crossing  the  anal  furrow 
near  the  margin  of  the  wing.  It  is  evident  that  the  forces 
that  are  causing  the  branches  of  the  cubitus  to  migrate  along 
the  first  anal  vein  and  towards  the  base  of  the  wing  are  ex- 
erting a  similar  influence  on  this  vein.  It  is  also  evident 
that  vein  M^  and  C«,  coalesce  at  the  tip,  and  that  the  migra- 
tion of  the  united  tips  of  these  veins  (marked  Cu  in  the  figure) 
towards  the  base  of  the  wing  has  so  modified  the  course  of 
that  part  of  vein  M^  which  is  still  free  that  this  part  of  this 
vein  extends  towards  the  base  of  the  wing.  This  change  is 
very  similar  to  the  change  in  the  course  of  vein  Cu^  in  the 
Empidid. 

A  curious  result  of  this  change  in  the  direction  of  the 
course  of  vein  M^  is  that  the  cell  M^  has  been  closed  and 

*  Comstock,  loc.  cit.  Fig.  735. 


io6 

pressed  back  to  the  centre  of  the  wing  (Fig.  7,  M^,  and  now 
lies  in  front  of  the  free  portion  of  the  vein  M^  instead  of  be- 
hind it.* 

Let  us  now  consider  the  courses  of  the  branches  of  the 
radius.  Here  again  we  can  gain  help  from  a  study  of  dip- 
terous wings.  Observe  in  the  Bombyliid  (Pantarbes)  the 
coalescence  of  the  tips  of  veins  R^  and  M^.  In  the  Hymen- 
optera  a  similar  coalescence  of  veins  R^  and  M^  has  occurred  ; 
but  it  has  proceeded  much  farther,  so  that  the  free  portion 
of  vein  R^  in  Pamphilius  (Fig.  6,  R^  is  remote  from  the  end 
of  the  wing  and  has  the  appearance  of  a  cross-vein. 

In  the  Hymenoptera  vein  R^  has  been  followed  in  its 
migration  along  vein  M^  by  vein  R^^  which  has  now  reached 
a  stage  in  Pamphilius  that  is  quite  similar  to  that  reached  by 
vein  R^  in  Pantarbes.  But  like  vein  R^  it  has  the  appearance 
of  a  cross-vein. 

From  this  it  will  be  seen  that  the  vein  marked  M^  in  Fig- 
ure 6  is  really  compound,  as  it  includes  the  tips  of  veins 
R^  and  R^. 

In  Pamphilius  vein  R^  is  curved  away  from  the  costal 
margin  of  the  wing  to  make  room  for  a  stigma  (Fig.  7,  S), 
and  vein  R^  ends  in  the  costal  margin  a  short  distance  before 
the  apex  of  the  wing  (Fig.  6).  Vein  R^  has  been  lost  in  this 
genus,  but  is  well  preserved  in  certain  closely  allied  forms.f 
and  is,  therefore,  represented  in  the  figure. 

While  the  tips  of  the  branches  of  the  radial  sector  have 
migrated  away  from  the  apex  of  the  wing,  the  bases  of 
these  branches  coalesce  in  the  opposite  direction  ;  from  these 

*  At  the  time  that  the  figures  in  Comstock's  Manual  were  prepared  it  was 
believed  that  the  media  was  typically  three-branched.  For  that  reason  the  vein 
which  we  now  regard  as  vein  M^  was  believed  to  be  a  cross-vein.  The  inter- 
pretation given  above  accords  better  with  what  we  have  since  learned  to  be  the 
fypical  form  of  the  media. 

t  See  page  103,  footnote. 


107 

two  causes  results  the  transverse  bracing  of  the  radial  area 
of  the  wing,  which  is  a  very  characteristic  feature  of  the 
venation  of  the  wings  in  this  order. 

The  details  of  these  changes  will  be  made  clear  by  an  ex- 
amination of  Figures  8  and  9.  The  former  represents  the 
primitive  mode  of  branching  of  the  radius  ;  the  latter,  the 
radial  area  of  the  typical  hymenopterous  wing  (Fig.  6).  In 
the  hymenopterous  type  veins  R^j^^  and  R^.^^  of  the  primitive 


/?,         Ri 


Fig.  8.— The  typical  radius. 


Fig.  9. — The  radius  in  Hymenoptera. 


type  coalesce  so  far  that  the  branches  of  the  sector  arise 
from  a  common  stem  ;  and  the  tips  of  all  of  them  have 
moved  away  from  the  apex  of  the  wing,  veins  R^  and  R^ 
following  the  costal  margin  of  the  wing  ;  and  veins  R^  and 
R^  following  vein  M^. 

In  the  Hymenoptera  the  radial  cross-vein  is  frequently 
preserved;  it  is  marked  ^  z'  in  figures  6  and  9. 

The  student  who  has  followed  this  discussion  and  has 
understood  it  will  be  prepared  to  make  original  investiga- 
tions of  the  venation  of  the  wings  of   Hymenoptera.     But  no 


io8 

student  should  take  up  the  work  indicated  below  before 
everything  in  this  discussion  is  clear  to  him. 

Study  the  fore  wings  of  the  insects  named  below.  It  is 
not  best  to  attempt  to  determine  the  homologies  of  the  veins 
of  the  hind  wings  at  first,  owing  to  the  great  reduction  of 
wing-veins  that  has  taken  place  in  these  wings.  The  direc- 
tions for  the  study  of  wings  given  on  page  97  will  apply  here 
except  that  Figures  6  and  7  instead  of  Figure  2  will  be  used 
for  comparison.     Indicate  the  media  with  red  ink. 

The  fore  wings  of  Tenthredinids. — The  wings  of  two 
sawflies  will  be  used  as  examples  of  different  degrees  of 
specialization  : 

(a.)  Macroxyela. 

(b.)  Fterojins.     The  currant  sawfly. 

The  fore  wing  of  a  Siricid. — The  best  genus  of  the 
Siricidae  for  this  study  is  Sirex.  The  more  common,  TremeXy 
is  more  difficult. 

The  fore  wing  of  a  Sphecid. — Use  for  this  purpose  a 
wing  of  the  common  mud-dauber,  Pelopaus. 

The  fore  wing  of  an  Ichneumon-fly.— A  species  of 
Ichneianon  will  furnish  an  example. 

The  fore  wing  of  a  Braconid. — Compare  with  the  wing 
of  an  Ichneumon-fly.  Color  vein  M^  red  and  the  medial 
cross  vein  black. 

The  fore  wing  of  the  Honey-bee. 

THE    WINGS    OF    NEUROPTERA. 

The  foregoing  studies  of  the  wings  of  Diptera,  Lepidop- 
tera,  and  Hymenoptera  have  shown  that  m  none  of  the 
genera  studied  has  the  number  of  the  branches  of  any  vem 
exceeded  that  of  our  hypothetical  type  (Fig.  5),  and  that  m 
none  of  them  have  all  of  the  branches  of  all  of  the  veins  re- 


109 

mained  distinct.     These  wings  illustrate,  therefore,  what  has 
been  termed  specialization  by  reduction. 

There  are,  however,  several  orders  of  insects  in  which,  as 
a  rule,  some  of  the  wing-veins  have  a  greater  number  of 
branches  than  in  the  hypothetical  type.  These  illustrate 
what  has  been  termed  specialization  by  addition. 

Among  the  orders  in  which  specialization  of  wing-veins 
by  addition  has  taken  place  is  the  Neuroptera  ;  and  several 
genera  of  this  order  will  be  studied  as  examples  of  this 
method  of  specialization.  We  will,  however,  first  point  out 
the  more  important  features  of  specialization  of  wing-veins 
by  addition. 

In  speaking  of  an  increase  in  the  number  of  veins,  refer- 
ence is  made  only  to  a  multiplication  of  the  branches  of  the 
principal  veins.  In  no  case  is  there  an  increase  in  the  num- 
ber of  principal  veins.  And  this  increase  in  the  number  of 
branches  may  be  confined  to  one  or  two  of  the  principal 
veins  in  the  preanal  area,  while  the  number  of  the  branches 
of  some  of  the  other  veins  may  be  reduced,  the  expanding 
of  some  parts  of  the  preanal  area  resulting  in  a  crowding  of 
other  parts.  In  some  cases  we  will  find  that  the  multiplica- 
tion of  wing-veins  extends  to  the  anal  area  also  ;  in  others 
we  will  find  the  anal  area  greatly  reduced.  But  even  in 
those  cases  where  the  anal  area  is  reduced,  the  total  result 
has  been  the  production  of  a  many-veined  wing. 

In  the  many-veined  wings  both  the  longitudinal  veins  and 
the  cross-veins  are  increased  in  number.  In  most  cases 
where  there  are  many  cross-veins  it  is  impracticable  to  dis- 
tinguish from  others  those  particular  cross-veins  to  which  we 
applied  special  names  in  describing  the  few-veined  wings. 
(See  page  91.)  But  in  the  case  of  the  longitudinal  veins  it 
is  necessary  to  distinguish  the  primitive  veins,  that  is,  those 
of  our  hypothetical  type,  from  the  veins  that  have  been  de- 
veloped in  addition  to  these.     For  if  this  is  not  done  it  will 


no 

be  impossible  to  point  out  the  changes  that  have  taken 
place  in  the  course  of  the  development  of  each  of  the  vari- 
ous types  of  many-veined  wings.  We  therefore  apply  the 
term  accessory  veins  to  these  secondarily  developed  longitu- 
dinal veins,  and  retain  the  same  nomenclature  for  the  primi- 
tive veins  that  we  used  in  describing  the  few-veined  wings. 

The  development  of  accessory  veins. — Accessory 
veins  may  be  borne  by  any  of  the  primitive  longitudinal 
veins ;  and  they  may  arise  from  either  of  the  two  sides  of 
such  a  vein.  In  most  cases  it  is  unnecessary  to  designate 
the  individual  accessory  veins,  as,  usually,  it  will  be  sufficient 
for  descriptive  purposes  to  indicate  the  number  of  these 
veins  that  have  been  developed  upon  a  particular  longitudi- 
nal vein.  In  fact,  in  certain  cases  more  than  this  could  not 
well  be  done,  owing  to  the  irregularity  of  the  veins.  On  the 
other  hand,  in  many  cases  the  accessory  veins  borne  by  a 
single  primitive  vein  present  a  high  degree  of  regularity, 
and  it  is  evident  that  they  have  been  developed  in  a  regular 
sequence.  Under  these  circumstances  it  is  practicable  to 
designate  them  individually  ;  and  we  have  devised  the  fol- 
lowing method  for  this  purpose. 

The  accessory  veins  arising  from  one  side  of  a  single 
primitive  vein  are  considered  as  a  single  set,  and  to  each  set 
of  veins  a  distinct  set  of  numbers  is  applied,  beginning  with 
the  oldest  {i.e.,  the  first-developed)  member  of  the  set. 

By  this  method  homologous  veins,  when  a  homology  ex- 
ists, will  bear  the  same  number.  But  it  should  be  remem- 
bered that  as  accessory  veins  have  arisen  independently  in 
many  different  groups  of  insects,  it  often  happens  that  acces- 
sory veins  similar  in  position,  and  bearing  the  same  number 
in  our  system,  are  merely  analogous  and  not  homologous. 

In  order  to  apply  this  system  it  is  necessary  to  know,  in 
the  case  of  each  group  of  insects  studied,  the  sequence  in 
which  the  members  of  the  particular  set  of  veins  under  con- 


Ill 


sideration  have  b^en  developed.  For  additions  to  such  a  set 
of  veins  may  be  made  to  the  distal  end  of  the  series,  or  to 
the  proximal  end,  or  may  be  interpolated  at  some  distance 
from  either  end. 

We  will  illustrate  these  principles  by  a  figure  of  the  wing 
of  a  nymph  of  a  cockroach  (Fig.  lo).  We  do  not  use  for  this 
purpose  a  figure  of  a  wing  of  a  neuropterous  insect,  as  that 
would  lessen  the  value,  as  a  means  of  training,  of  the  study 
of  neuropterous   wings  which  the  student  is  to  make.      A 


Fig.  10. — Hind  wing  of  a  nymph  of  a  cockroach. 

nymph  is  used  here,  because  in  the  many-veined  insects  the 
longitudinal  veins,  both  primitive  and  accessory,  are  devel- 
oped about  tracheae  ;  and  it  is  much  easier  to  determine  the 
homologies  of  the  tracheae  of  an  immature  wing  than  it  is  to 
determine  the  homologies  of  the  wing-veins  of  the  adult. 
And,  too,  in  this  way  we  are  able  to  eliminate  the  cross- 
veins  which  are  not  preceded  by  tracheae  in  the  cockroaches. 
Accessory  veins  added  distally. — If  the  radial  trachea  of  the 
nymph  of  a  cockroach  be  examined  (Fig.  lo,  /?),  it  will  be 
seen  that  it  bears  many  branches  on  its  cephalic  side  ;  each 
of  these  branches  is  enclosed  by  a  vein  in  the  adult  state. 
The  number  of  these  veins  is  much  greater  than  that  of  the 


112 

hypothetical  type.  A  comparison  of  the  wings  of  different 
species  of  cockroaches  shows  that  the  increase  in  the  num- 
ber of  the  branches  of  the  radius  has  been  greater  in  some 
than  in  others  ;  and  a  study  of  the  one  figured  indicates  the 
method  of  increase,  which  is  doubtless  as  follows  :  the 
branches  have  been  added,  one  after  another,  to  the  tip  of 
the  trachea,  R,  there  being  a  migration  of  the  base  of  each 
accessory  trachea  towards  the  base  of  the  wing,  thus  making 
room  for  the  addition  of  new  branches.  In  this  case  the 
first  accessory  vein  is  the  proximal  one  ;  but  in  this  particu- 
lar instance  it  is  impracticable  to  number  the  accessory 
veins,  owing  to  a  splitting  of  some  of  them  which  is  taking 
place. 

.  Accessory  veins  added  proximally. — A  study  of  the  cubital 
trachea  of  the  nymph  of  the  cockroach  figured  above  (Fig. 
lo,  Cii)  shows  that  accessory  veins  are  being  developed  on 
the  caudal  side  of  vein  C//,.  It  can  also  be  seen  that  the 
distal  members  of  the  serres  of  accessory  tracheae  are  well- 
developed,  and  that  the  growth  of  additional  ones  is  taking 
place  in  the  disk  of  the  wing  at  the  proximal  end  of  the 
series.  In  this  case  the  first  accessory  vein  is  the  distal  one, 
and  the  accessory  veins  should  be  numbered  as  indicated  in 
the  figure. 

Accessory  veins  interpolated. — Reference  has  been  made  above 
to  a  splitting  of  some  of  the  accessory  tracheae  developed  on 
the  cephalic  side  of  the  radial  trachea  in  the  cockroach  under 
consideration  (Fig.  lo).  As  a  vein  is  developed  about  each 
of  the  divisions  of  these  tracheae,  it  is  evident  that  at  the 
same  time  that  accessory  veins  are  being  added  distally  to 
this  series  others  are  being  interpolated.  In  cases  of  this 
kind  it  is  impracticable  to  number  the  members  of  a  series  of 
accessory  veins. 

The  suppression  of  the  dichotomous  branching  of 
veins. — In  the  more  highly  specialized  of  the  many-veined 


113 


insect  wings  there  exists  a  type  of  branching  which  is  very 
different  from  that  of  our  hypothetical  primitive  type.  An 
examination  of  Figure  5,  which  represents  the  latter,  will  show 
that  in  every  case 
the  forked  veins  are 
branched  dichoto- 
mously,  while  in  the 
many-veined  wings 
the  more  character- 
istic type  of  branch- 
ing results  in  the 
formation  of  pecti- 
nate veins;  this 
pectinate  type  of 
branching  is  well 
shown  by  the  cubi- 
tus in  a  cockroach 
(Fig.  10  Cu). 

The  changes  that 
take  place  in  the 
development  of  the 
pectinate  type  of 
venation  from  the 
dichotomous  type 
are  of  two  kinds  : 
first,  the  develop- 
ment of  accessory 
veins  ;  second,  the 
modification  of  the 
primitive  veins  so 
that    they    are    no 

longer  dichotomously  branched.  The  former  has  been  dis- 
cussed above  ;  we  will  now  briefly  refer  to  the  latter.  For 
this  purpose  we  will  give  a  series  of  diagrams  illustrating 


Fig.  II. — Diagrams  of  several  types  of  radius. 


114 

several  types  of  branching  of  the  radial  sector.  Each  of 
these  figures  represents  a  condition  which  exists  in  some 
insect. 

Figure  iia  represents  the  typical  or  dichotomously 
branched  radial  sector.  Figure  ii^  represents  a  typical  ra- 
dial sector  with  the  addition  of  some  accessory  veins  on  the 
caudal  side  of  vein  J^^.  In  this  case  the  radial  sector  is 
nearly  pectinate,  but  not  quite  so,  owing  to  the  forked  con- 
dition of  vein  -^4+5.  In  the  form  represented  by  Figure  iic 
veins  J?^  and  J?^  coalesce  to  the  margin  of  the  wing  ;  and  in 
this  way  the  pectinate  type  is  attained.  In  another  insect 
(Fig.  lid)  the  pectinate  type  has  been  attained  by  fission  in- 
stead of  coalescence.  Here  veins  J?^  and  7?^  have  split  apart 
till  vein  J?^  arises  from  the  main  stem  of  radius. 

When  many  cross-veins  are  present,  the  dichotomy  of  the 
branching  of  the  sector  may  be  suppressed  in  still  another 
way,  by  the  transference  of  the  base  of  vein  J?^  to  vein 
^^+3.  All  stages  of  this  switching  of  the  base  of  vein  R^ 
occur  in  the  ant-lions  ;  and  two  of  them  are  represented  by 
Figures  zie  and  11/. 

In  the  genus  represented  by  Figure  ik?  the  base  of  vein 
i?^  appears  to  be  forked  ;  one  arm  of  the  fork  arising  from 
vein  J^^,  the  other  from  vein  ^^+3.  The  former  is  the  true 
base  of  vein  i?^  ;  the  latter  is  a  cross-vein  which  is  assuming 
the  function  of  a  base  of  this  vein.  In  the  genus  repre- 
sented by  Figure  11/  the  switching  has  been  completed, 
vein  J?^  arising  from  vein  J^^^y 

In  the  foregoing  illustrations  comparisons  of  allied  insects 
have  been  made  in  order  to  determine  the  ways  in  which 
the  wings  are  being  modified  ;  frequently  a  comparative 
study  of  the  fore  and  hind  wings  of  a  single  insect  is  equally 
suggestive,  for  it  often  happens  that  the  two  pairs  of  wings 
exhibit  different  degrees  of  the  same  kind  of  modification, 
and  thus  the  course  of  the  change  is  indicated. 


115 

A  study  of  the  causes  of  the  changes  which  we  are  de- 
scribing is  beyond  our  present  purpose,  which  is  merely  to 
determine  the  homologies  of  the  wing-veins.  But  we  can 
gain  a  hint  of  the  probable  reason  for  the  development  of 
the  pectinate  type  of  veins  without  entering  very  deeply  into 
questions  of  the  mechanics  of  flight. 

It  is  obvious  that  many  styles  of  flight  exist  among  in- 
sects, and  that  for  the  different  styles  of  flight  different 
kinds  of  wings  are  required.  In  Corydalis,  which  will  be 
studied  a  little  later,  it  can  be  seen  that  the  wing  is  stiffened, 
along  a  line  parallel  with  the  costal  margin  of  the  wing,  by 
the  subcosta,  the  main  stem  of  the  radius,  and  veins  R^  and 
R^.  Back  of  this  line  there  is  a  broad,  flexible  area,  which 
bends  up  during  the  downward  stroke  of  the  wing,  forming 
an  inclined  plane,  the  pressure  of  which  against  the  air 
forces  the  insect  ahead.  The  flexibility  of  this  area  of  the 
w'ing  is  increased  by  those  changes  which  result  in  the  for- 
mation of  the  pectinate  type  of  branching. 

The  wings  of  Sialis. — Among  our  more  common  neu- 
ropterous  insects  those  of  the  genus  Sialis  have  retained  the 
most  generalized  condition  of  wing-venation.  It  is  sug- 
gested, therefore,  that  the  student  begin  his  practice  in  de- 
termining the  homologies  of  the  wing-veins  of  Neuroptera 
with  a  member  of  this  genus.  Make  a  drawing  of  the  wings 
and  letter  the  principal  veins,  and  the  accessory  veins. 

The  wings  of  Chauliodes. — 

The  wings  of  Corydalis. — In  this  genus  the  radial  sec- 
tor is  an  example  of  a  high  development  of  the  pectinate 
type  of  venation. 

The  wings  of  Ant-lions. — Photographs  of  the  wings  of 
representatives  of  several  genera  of  the  Myrmeleonidae  will 
be  furnished  the  student  for  study.  The  photographs  repre- 
sent the  wings  greatly  enlarged  and  are,  therefore,  much 
more   available    for   study    than    the   actual    wings.       Each 


ii6 

'  photograph  is  labeled  with  the  name  of  the  genus  it  repre- 
sents. 

Spread  out  the  photographs  before  you  and  study  the 
costal  area  of  the  wings  ;  the  costal  area  is  the  area  between 
the  costa  and  the  subcosta  ;  it  corresponds  to  cell  C  of  the 
few-veined  insects.  Observe  the  varying  degrees  of  com- 
plexity of  the  cross-veins  ;  observe  also  the  stiffening  of  the 
area  opposite  the  point  where  veins  Sc  and  R  coalesce,  and 
compare  it  with  the  stigma  in  the  Hymenoptera. 

Study  the  radial  area  of  all  of  the  wings,  determine  the 
homologies  of  the  branches  of  the  radius  in  each,  letter 
them,  and  number  the  accessory  veins.  Also  indicate  with 
pencil  marks  the  way  in  which  the  suppression  of  the  dichot- 
omous  branching  has  been  brought  about. 

That  part  of  the  wing  of  these  insects  lying  caudad  of  the 
radius  presents  difficulties  that  could  hardly  be  solved  by  a 
study  of  adults  alone.  A  study  of  the  development  of  the 
wings  of  an  ant-lion  has  shown  that  the  second  of  the  two 
principal  branches  of  the  media  and  vein  C//,  coalesce. 
Study  the  fore  wings,  which  are  less  modified  than  the  hind 
wings,  and  observe  that  the  media  appears  to  be  a  simple 
vein  for  the  greater  part  of  its  length,  and  that  the  cubitus 
exhibits  a  well-marked  fork  before  the  middle  of  the  wing. 
This  fork  is  the  point  of  separation  of  veins  C//,  and  Cu^. 
Observe  that  near  this  forking  of  the  cubitus  there  is  what 
appears  to  be  an  oblique  cross-vein  extending  from  the  media 
to  the  cubitus  ;  this  is  not  a  cross-vein,  but  is  the  beginning 
of  vein  M^j^^,  which  coalesces  with  vein  Cu^  for  the  greater 
part  of  its  length.  Letter  the  branches  of  the  media  and  of 
the  cubitus  on  each  photograph.  After  this  work  has  been 
criticised,  trace  the  course  of  media  with  red  ink  and  the 
courses  of  radius  and  cubitus  with  black  ink,  omitting  the 
accessory  veins. 


117 


THE      TRACHEATION      OF      THE      WINGS     OF      NYMPHS     AND     OF 

PUP/E. 

It  has  been  found  that,  in  the  course  of  the  development 
of  the  wings  of  the  more  generalized  insects,  the  trachese 
which  traverse  the  principal  veins  are  developed  before  the 
veins  appear,  and  that  later  the  veins  are  developed  about 
these  tracheae.  It  is  evident,  therefore,  that  much  light 
can  be  thrown  upon  questions  regarding  the  homologies  of 
wing-veins  by  studies  of  the  tracheae  which  precede  them  ; 
and  the  following  suggestions  are  given  to  aid  students  who 
wish  to  make,  such  studies. 

If  a  living  pupa  or  nymph  be  placed  in  formol  (4^)  the 
tissues  of  the  wings  will  be  rendered  translucent  in  a  short 
time.  In  the  case  of  very  delicate  insects  only  a  few  hours 
are  required  for  this,  but  with  larger  ones  with  more  opaque 
wings  it  is  necessary  to  leave  them  in  the  formol  for  several 
days,  or  even  for  several  weeks.  While  the  formol  renders 
the  tissues  translucent,  it  does  not  soon  penetrate  the 
tracheae,  which  are,  therefore,  left  filled  with  air,  and  appear 
as  dark  lines  when  the  wing  is  examined  with  transmitted 
light.  Just  after  molting  some  wings  are  translucent,  but 
there  are  few  so  clear  that  a  short  stay  in  formol  will  not 
make  them  clearer. 

In  order  to  study  wings  prepared  in  this  way,  they  are 
removed  from  the  body  and  mounted  in  glycerine-jelly,  care 
being  taken  to  cool  the  mount  quickly  so  that  the  jelly  will 
not  penetrate  the  tracheae.  In  this  way  most  beautiful 
objects  can  be  prepared,  which  will  show  the  minutest  rami- 
fications of  the  tracheae. 

Not  only  can  the  tracheae  that  precede  the  wing  veins  be 
studied  in  this  manner,  but,  if  the  wings  be  taken  at  the 
right  stage,  the  forming  veins  will  appear  as  pale  bands 
when   viewed  by  transmitted  light.     This  is  due  to  the  fact 


ii8 

that  at  this  time  the  veins  are  merely  cavities,  filled  with 
lymph,  and  are  more  translucent  than  the  spaces  between 
them,  which  are  occupied  by  tissue. 

Unfortunately,  however,  this  distinction  is  only  temporary 
in  most  specimens.  As  a  rule,  the  entire  wing  becomes 
transparent  in  a  few  hours  after  it  is  mounted  in  the  glyce- 
rine-jelly. It  is  necessary,  therefore,  to  make  drawings  or 
photo-micrographs  promptly,  in  order  to  keep  a  record  of 
the  courses  of  the  veins. 

On  the  other  hand,  the  tracheae,  as  a  rule,  stand  out  more 
sharply  twenty-four  hours  after  mounting,  because  of  the 
clearing  effect  of  the  glycerine-jelly  upon  the  tissue  of  the 
wing.  But  the  making  of  drawings  or  photo-micrographs 
of  the  tracheae  should  not  be  delayed  long  ;  for  the  tracheae 
soon  become  filled  with  the  jelly,  and  are  then  practically 
invisible. 

The  preparation  of  specimens.— Collect  living  nymphs 
or  pupae,  place  them  in  formol  (4^),  and  leave  them  for  a 
time,  as  indicated  above.  The  formol  will  make  the  wings 
of  the  insects  more  translucent  ;  but  it  will  not  remove  dark 
colors  from  chitin.  It  is  well,  therefore,  to  select,  at  first, 
the  paler  species  for  study. 

When  ready  to  mount  a  wing,  spread  a  drop  of  melted 
glycerine-jelly  on  a  slide  and  allow  it  to  cool. 

Dissect  off  the  wing  to  be  studied,  taking  with  it  just 
enough  of  the  thorax  to  include  the  basal  attachments  of  the 
tracheae.  The  dissection  may  be  made  under  water  ;  but  the 
wing  should  be  removed  from  the  water  promptly,  so  that  the 
tracheae  may  not  become  filled  with  water. 

Place  the  wing"  upon  the  solidified  glycerine-jelly  on  the 
slide  ;  and  lower  upon  it  a  heated  cover-glass,  which  will 
cause  the  jelly  to  melt  enough  to  envelop  the  wing. 

Cool  the  mount  quickly  on  ice,  a  marble  slab,  or  some  other 
cold  object.     Rapid  cooling  is  imperative,  for  in  melted  glyc- 


119 

erine-jelly  the  tracheae  soon  become  filled,  and  the  smaller 
ones  are  then  invisible. 

It  is  imperative,  also,  that  the  wings  be  handled  with  care. 
Being  sac-like  structures,  the  tracheae  are  almost  free  within 
them,  and  a  slight  pinch  with  forceps  in  the  middle  of  the 
wing  may  throw  all  of  its  tracheae  out  of  place.  It  is  better 
to  lift  the  wing  by  its  thoracic  attachments  or  upon  a  section 
lifter. 

Not  every  nymphal  wing  is  fitted  for  this  study.  Just  before 
molting,  and  especially  just  before  the  last  molting,  the  wing 
becomes  so  crumpled  within  its  old  sheath  that  the  course  of 
its  tracheae  can  be  followed  only  with  difficulty. 

The  method  of  study. — So  far  as  is  practicable,  the 
studies  of  the  tracheation  of  the  wings  of  nymphs  and  of 
pupae  will  be  original  investigations.  For  this  reason,  no 
particular  species  is  suggested  for  study.  The  student  will 
select  the  most  available  material,  and  will  endeavor  to  make 
an  addition  to  our  knowledge  of  this  subject.  The  series  of 
articles  in  the  Aitierican  Naturalist,  already  referred  to  (see 
page  '^^,  note),  may  be  used  as  a  work  of  reference.  A  few 
suggestions,  drawn  from  the  studies  upon  which  those  arti- 
cles were  based,  are  given  here  : — 

Among  the  more  available  subjects  for  the  beginner  in 
this  line  of  work,  are  the  pupae  of  moths  and  the  nymphs  of 
Orthoptera.  The  former  illustrate  specialization  by  reduc- 
tion ;  the  latter  specialization  by  addition.  During  the  win- 
ter, when  it  is  difficult  to  collect  Orthoptera,  the  nymphs  of 
stone-flies  (Plecoptera)  may  be  used  instead.  These  can  be 
found  under  stones  in  the  beds  of  streams. 

In  many  insects  the  costal  trachea  is  wanting  or  is  but 
slightly  developed.  It  does  not  follow,  therefore,  that  the 
trachea  nearest  the  costal  margin  of  the  wing  is  the  costal 
trachea.  In  most  cases,  the  radial  trachea  can  be  identi- 
fied easily,    and    it    will  serve  as   a    starting   point   for  the 


I20 

determination   of   the   homologies   of    the    other    principal 
tracheae. 

In  most  orders  of  insects  the  longitudinal  veins  can  be 
distinguished  from  the  cross-veins  by  the  fact  that  the  cross- 
veins  are  not  preceded  by  tracheae. 

In    some   of   the    many-veined    insects,    as   Odonata,    the 
cross-veins,  as  well  as  the  longitudinal  veins,  are  preceded 
by  tracheae  ;  there  being,  in  these  insects,  a  great  multiplica-- 
tion  of  tracheae. 

On  the  other  hand,  in  the  Trichoptera,  Diptera,  and  most 
Hymenoptera,  a  great  reduction  of  the  tracheal  system  has 
taken  place.  It  is  not  well,  therefore,  for  the  student  to 
begin  his  studies  of  this  subject  with  members  of  either  of 
these  orders. 

In  those  orders  where  a  specialization  of  wing-veins  by 
addition  has  taken  place,  the  accessory  longitudinal  veins  are 
preceded  by  tracheae. 

Finally,  it  should  be  remembered  that  it  is  not  safe  to  base 
conclusions  upon  the  study  of  a  single  insect ;  a  large  series, 
representing  as  many  genera  and  families  as  is  practicable, 
should  be  investigated. 


CHAPTER   VIII 
METHODS   OF   INSECT  HISTOLOGY. 
INTRODUCTION. 

The  study  of  the  gross  anatomy  of  most  insects  requires 
no  more  in  the  way  of  equipment  than  a  simple  dissecting 
outfit, — viz.,  scalpels,  scissors,  needles,  and  dissecting  tray ; 
and  little  more  in  the  way  of  method  than  skilful  manipula- 
tion of  these  simple  tools.  But  for  the  study  of  the  anatomy 
of  very  small  insects,  and  more  especially  for  the  study  of 
the  histology  of  insect  organs,  the  character  of  the  various 
body-tissues,  the  histolytic  and  histogenetic  phenomena  ac- 
companying the  post-embryonal  growth  of  insects  with  com- 
plete metamorphosis,  and,  finally,  for  the  study  of  insect 
embryology,  a  more  elaborate  equipment  is  required,  and 
some  knowledge  of  the  special  methods  of  the  animal  his- 
tologist  is  needed. 

Insects  present  a  special  problem  in  histologic  method 
because  of  the  always  present  covering  of  chitin  which  pro- 
tects their  bodies.  This  chitinous  wall  hinders  very  effect- 
ively the  penetration  of  the  fixing  fluids  and  besides  presents 
very  serious  difficulties  in  section  cutting.  Hence  even  the 
student  already  familiar  with  the  usual  methods  of  animal 
histology  needs  some  special  guiding  in  beginning  the  study 
of  insect  histology. 

The  following  notes  are  intended  to  furnish  a  guide  for 
beginning  students  of    insect    histology  and  development. 


122 

For  advanced  students,  needing  a  knowledge  of  more  special 
methods,  Lee's  Microtomist's  Vade-Mecum  (5th  edition,  1900), 
and  the  notes  of  "  technic  "  given  in  the  many  papers  treating 
of  insect  histology  and  development  will  furnish  valuable  sug- 
gestions. All  of  the  general  methods  of  killing,  fixing, 
staining,  etc.,  given  in  the  following  notes  have  been  person- 
ally used  by  the  authors  in  studying  insects.  For  those  few 
special  cases  of  treatment  of  particular  tissues  and  organs 
introduced,  which  have  not  been  tried  by  the  authors,  an 
authoritative  reference  to  the  use  of  the  method  is  always 
given. 

It  is  hardly  necessary  to  say  that  within  certain  limits 
there  is  a  great  deal  of  difference  in  the  practice  of  microto- 
mists  in  the  matter  of  method.  In  these  brief  notes  it  is  in- 
tended to  outline  a  simple,  straightforward  course  of  proced- 
ure which  has  been  found  by  actual  work  on  insect  tissues  to 
give  good  results  in  such  work.  Even  this  plan  has  been 
found  difficult  to  adhere  to,  because  a  certain  amount  of 
variation  is  sure  to  enter  into  the  practice  of  any  worker. 
The  student  will  find  out  for  himself,  however,  as  he  gets 
more  and  more  familiar  with  the  work,  the  advantages  of 
variation,  and  will  be  able  to  take  advantage  of  the  oppor- 
tunities for  modifying  his  practice  presented  by  the  many  (at 
first  glance,  confusingly  many)  suggestions  of  the  standard 
manuals  of  microtomic  technic.  The  following  three  books 
will  be  of  special  value  for  reference. 

Lee,  A.  B. :  The  Microtomist's  Vade-Mecum^  5th  edition, 
1900. 

Whitman,  C.  O.:  Method  of  Research  in  Microscopical 
Anatomy  and  Embryology,  1885. 

Gage,  S.  H.:      The  Microscope,  7th  edition,  1901. 


123 


MATERIAL    FOR    STUDY. 

For  general  histology. — Any  organs  or  tissues  desired 
for  study  should  be  dissected  out  of  a  specimen  which  has 
been  made  insensible  by  chloroform  or  ether  or  cocaine  or 
which  has  just  been  killed  by  some  quick  process.  The 
point  is  to  get  the  material  in  a  fresh  and  perfectly  normal 
condition.  The  tissue  must  be  alive  at  the  time  it  goes  into 
the  fixing  fluid.  A  certain  way  of  accomplishing  this  is  to 
kill  the  insect  by  dropping  it  into  the  fixing  fluid.  But  that 
the  tissue  may  certainly  be  reached  and  affected  by  the  fluid, 
the  specimen,  unless  small  and  with  very  weakly  chitinized 
integument,  must  be  cut  open. 

For  studying  anatomy  or  development. — It  is  often 
desirable  to  make  serial  sections  of  the  whole  body  of  an  in- 
sect. In  the  case  of  insex:ts  too  small  to  dissect  this  is  the 
only  means  of  studying  their  anatomy.  In  the  study  of  the 
post-embryonal  development  of  insects  which  have  complete 
metamorphosis,  the  advanced  larval  and  the  pupal  stages 
must  be  examined  by  such  sections,  because  of  the  great 
breaking  down  of  many  of  the  body-tissues.  Specimens 
should  be  killed  immediately  after  moulting,  when  the  outer 
chitin  wall  is  thinnest  and  most  pervious  to  the  fixing  liquids. 
By  rearing  the  specimens,  just  moulted  larvae,  just  formed 
pupae,  and  just  issued  imagines  may  be  obtained,  and  the  use 
of  such  specimens  will  be  found  to  be  immensely  advan- 
tageous. Strongly  chitinized  specimens,  which  must  be  sec- 
tioned, may  be  carefully  and  cleanly  cut  into  two  or  three 
parts,  say,  head,  thorax,  and  abdomen.  This  will  enable  the 
fixing  fluids  to  penetrate  the  body  cavity,  although  the  diffi- 
culty of  cutting  the  firm  chitin  wall  with  the  microtome  knife 
still  remains.  Certain  methods  of  softening  the  chitin  are 
used  by  some  workers,  but  there  is  always  danger  in  the 
practice  of  injuring  the  other  more  delicate  tissues. 


124 

For  embryology. — In  obtaining  insect  eggs  it  is  highly 
desirable,  often  imperatively  necessary,  to  know  the  exact 
age  of  the  specimens.  Hence  it  is  desirable  to  capture 
females  of  the  species  to  be  studied,  and  if  possible  have  the 
eggs  laid  in  captivity.  Thus  the  exact  time  of  oviposition, 
and  consequently  the  age  of  the  specimens  studied,  can  be 
known.  For  work  simply  illustrative  of  the  embryologic 
development  of  insects,  eggs  should  be  chosen  which  are 
large,  and  are  not  spherical,  but  of  such  shape  that  the  speci- 
mens can  be  readily  oriented  at  the  time  of  imbedding  or 
cutting. 

PREPARATION    OF    MATERIAL    FOR    SECTIONING. 

The  sequence  of  treatment. — The  fresh,  live  mate- 
rial (bits  of  tissue,  organs,  whole  insects,  or  eggs),  which  is  to 
be  studied  by  means  of  sections,  must  undergo  certain  treat- 
ment necessary  to  preserve  it,  and  to  prepare  it  for  cutting. 
It  has  first  to  be  killed  zn6.  fixed  j  next  to  be  hardened;  next 
to  be  cleared;  and  finally  to  be  infiltrated  with  and  imbedded 
in  paraffin  (or  collodion,  see  note  later).  (See  also  Recapit- 
ulation, p.  138.) 

Killing  and  fixing. — Out  of  the  bewildering  array  of 
fixing  agents,  the  student  of  insect  histology  must  choose  a 
few  which  are  characterized  by  great  penetrating  power. 
Many  of  the  commonly  used  agents  for  fixing  animal  tissues 
in  general  cannot  be  used  in  work  with  insects  (except  where 
dissected-out,  non-chitinous  organs  or  tissues  are  being  han- 
dled), because  of  their  inability  to  penetrate  the  chitinized 
integument. 

In  fixing,  a  relatively  large  amount  of  the  fixing  agent 
should  be  used,  say  at  least  50  times  the  volume  of  the 
specimens.  The  objects  should  sink,  if  not  at  first,  then 
later,  in  the  fixing  fluid.  If  the  objects  persist  in  floating 
they  probably  contain  air,  and  the  tissues  adjoining  air  bub- 


125 

bles  will  not  be  fixed.     The  use  of  heat  as  suggested  in  a 
later  note  may  expel  the  air. 

It  is  our  practice  to  divide  our  material  into  at  least  two 
similar  lots,  three  or  even  four  if  there  are  plenty  of  speci- 
mens, and  to  use  a  different  fixing  agent  for  each  of  these 
lots.  For  one  lot  use  a  sublimate  solution,  for  another  a 
chromic  acid  solution,  and  so  on.  This  not  only  gives  a 
variety  of  fixation,  but  insures  against  total  loss  in  the  event 
of  accident  to  one  of  the  lots. 

Boiling  water. — Drop  the  live  insects  into  boiling  water, 
or  put  them  into  a  glass  beaker  and  pour  boiling  water  over 
them.  Leave  the  specimens  in  the  hot  water,  without  further 
heating  it,  for  two  to  five  minutes.  Then  remove  to  30^ 
alcohol  for  three  hours,  then  to  50^  alcohol  for  three  hours, 
then  to  70^  alcohol  for  twelve  hours,  finally  into  85^  alcohol 
for  keeping.  Or  the  insects  may  be  killed  in  hot  water  and 
then  removed  to  any  one  of  the  fixing  agents  described  in 
the  following  paragraphs.  This  is  probably  the  best  way  of 
handling  whole  insects.  The  method  of  primarily  fixing  by 
boiling  water  is  especially  valuable  for  eggs  and  pupae,  which, 
owing  to  the  impervious  character  of  their  chitin-armor,  can 
hardly  be  fixed  in  any  other  way,  but  we  find  that  it  gives 
excellent  results  in  almost  all  general  work. 

Picro-aceto-siiblimate . — This  useful  fixing  agent  is  made  by 
taking  of  a  cold  saturated  solution  of  picric  acid  in  70^  alco- 
hol, one  part  ;  of  hot  saturated  aqueous  solution  of  corrosive 
sublimate,  one  part ;  and  a  few  drops  (^4  to  \f)  of  glacial 
acetic  acid.  The  fresh  tissue  or  live  insect  should  be  dropped 
into  this  fluid  and  allowed  to  remain  for  from  twelve  to 
twenty-four  hours  (incline  toward  the  longer  time).  Remove 
to  7o<^  alcohol  for  twenty-four  hours.  (The  alcohol  will 
slowly  remove  the  picric  acid,  and  should  be  changed  two  or 
three  times.  If  warm  alcohol  is  used  the  removal  of  picric 
acid  will  be  more  speedily  accomplished.)     Then  remove  to 


126 

S^fo  alcohol,  changing  once  or  twice  if  the  alcohol  becomes 
discolored.  It  is  not  necessary  to  remove  all  the  picric  acid 
before  proceeding  to  the  further  preparation  of  the  speci- 
mens. 

Picro-sulpJmric  acid. — Distilled  water  loo  parts,  sulphuric 
acid  2  parts,  picric  acid  as  much  as  will  dissolve.  Treat 
specimens  as  for  picro-aceto-sublimate. 

Merciiro-nitric  mixture. — Distilled  water,  400  c.c. ;  alcohol, 
60^  strength,  50  c.c. ;  nitric  acid,  46^  strength,  7  c.c. ;  glacial 
acetic  acid,  2  c.c. ;  corrosive  sublimate,  9  grams.  Leave  speci- 
mens in  this  mixture  for  from  three  to  twelve  hours  ;  twenty- 
four  may  be  better  in  some  cases.  Wash  in  70^^  alcohol  and 
remove  to  fresh  70^  alcohol,  to  which  a  small  amount  of 
tincture  of  iodine  has  been  added  to  hasten  the  removal  of 
the  corrosive  sublimate  ;  leave  in  this  solution  for  two  or 
three  days  and  then  transfer  to  85^  alcohol  for  indefinite 
keeping. 

Chromo-nitric  acid. — Alcohol,  70^  strength,  3  parts  ;  nitric 
acid,  10^  strength,  4  parts  ;  chromic  acid  ^^  strength,  3 
parts.  Leave  specimens  in  this  mixture  four  to  eight 
hours,  and  wash  in  70^  alcohol.  Leave  in  70^  alcohol  for 
twenty-four  hours,  and  remove  to  85^^  alcohol  for  keep- 
ing. 

Penetration  can  be  more  certainly  effected  if  the  fixing 
fluid  is  used  warm.  Where  the  killing  is  done  in  the  labo- 
ratory and  the  fluid  can  be  readily  slightly  heated,  it  is  well 
always  to  do  it. 

In  addition  to  the  fixing  agents  of  which  formulae  have 
been  given,  other  fixing  agents,  a  host  of  which  are  described 
in  chapters  IV.  and  V.  of  Lee's  Vade-Meciim,  may  be  used. 
For  cytological  work,  the  osmic  acid  agents,  such  as  Flem- 
miiig's  chromo-aceto-osmic  acid  (Lee's  Vade-Mecum,  p.  40),  and 
Hermann's  platino-aceto-osmic  acid  (Lee's  Vade-Mecum,  p.  45), 
should  be  used. 


127 

Hardening. — After  killing  and  fixing  and  washing  the 
specimens  are  kept  in  alcohol  of  85^  strength.  The  speci- 
mens may  be  kept  thus  indefinitely.  Specimens  which  are 
to  be  prepared  for  immediate  cutting  must  now  be  hardened. 
(If  the  specimens  are  to  be  stained  ///  toto,  the  staining  should 
now  be  done  before  removal  to  the  95^  alcohol.  For  direc- 
tions, see  p.  137.)  Remove  the  specimens  to  95^  alcohol 
and  leave  for  twenty-four  to  forty-eight  hours,  depending 
upon  size  of  specimen  and  degree  of  chitinization  of  integu- 
ment. Then  remove  to  absolute  alcohol  for  from  twenty- 
four  to  forty-eight  hours.  The  specimens,  if  properly  fixed, 
will  now  be  thoroughly  hardened. 

Clearing. — (For  theory  and  practice  of  clearing,  see  Lee's 
Vade-Mecum,  p.  64  et  scq.)  Remove  the  specimens  from  ab- 
solute alcohol  to  a  vial  which  has  been  half-filled  with  xylol 
and  then  filled  with  absolute  alcohol.  Put  the  specimens 
into  the  vial  and  leave  them  for  twelve  to  twenty-four  hours. 
Then  remove  to  a  vial  filled  with  xylol  and  leave  them 
until  cleared.  This  will  require  from  twelve  to  twenty-four 
hours. 

We  have  used  cedar-wood  oil  a  great  deal  for  clearing,  as 
follows  :  Remove  the  specimens  from  absolute  alcohol  to  a 
mixture  of  absolute  alcohol,  one  part,  cedar-wood  oil,  one 
part,  for  twenty-four  hours.  Then  remove  to  pure  cedar- 
wood  oil  for  twenty-four  hours. 

Chloroform,  which  has  been  much  used,  is  rather  decried  by 
the  present-day  workers.  For  insects  it  should  be  avoided, 
as  it  has  little  penetrating  power. 

Infiltrating  with  paraffin,  and  imbedding. — After 
clearing,  the  specimens  are  to  be  infiltrated  with  melted 
paraffin.  The  specimens  should  be  removed  from  the  vial 
of  cedar-wood  oil  or  xylol  into  a  small  dish  (watch-glass, 
beaker,  evaporating  dish,  casserole,  tin  *'pattie"  dish),  into 
which  part  of  the  cedar-wood  oil  or  xylol  from  the  vial  is 


128 

poured.  Place  this  dish  on  top  of  the  paraffin*  oven  (a 
water-bath  oven  heated  at  a  constant  temperature,  a  little 
above  the  melting  point  of  the  paraffin  used)  and  drop  into 
it  several  small  pieces  of  paraffin.  This  paraffin  will  slowly 
dissolve  in  the  cedar-wood  oil  or  xylol  and  this  mixture  will 
penetrate  the  specimens.  After  the  paraffin  is  all  dissolved, 
add  more  paraffin  and  remove  the  dish  to  the  interior  of  the 
oven.  Leave  here  for  from  three  to  six  hours,  depending  on 
size,  and  density,  of  chitinous  integument.  Then  remove 
the  specimens  to  a  similar  small  dish  of  melted  pure  paraffin 
and  keep  in  the  oven  for  from  six  to  twenty-four  hours. 
The  kind  of  paraffin  to  use  depends  largely  upon  the  charac- 
ter of  the  specimens.  For  very  delicate  specimens,  a  paraffin 
of  low  melting  point  is  desirable.  But  for  most  insect  work 
a  hard  paraffin  is  desirable,  say  paraffin  of  melting  point  of 
about  55°  Centigrade.  In  the  summer,  hard  paraffin  must  be 
used  for  the  sake  of  ease  in  cutting. 

Another  common  method  of  infiltrating  with  paraffin  is  to 
remove  the  specimens  from  pure  xylol  or  cedar-wood  oil  to  a 
mixture  (prepared  beforehand)  of  one-half  paraffin  and  one- 
half  xylol  or  cedar-wood  oil.  Leave  in  this  mixture,  in  the 
oven,  for  from  three  to  six  hours,  and  then  remove  to  pure 
melted  paraffin  and  leave,  in  the  oven,  for  from  six  to  twenty- 
four  hours. 

After  the  objects  are  thoroughly  infiltrated  with  pure 
paraffin  they  must  be  imbedded.  Make  a  small  oblong 
paper  tray  (see  Lee's  Vade-Mecum,  p.  91)  and  pour  into  it  a 
little  melted  pure  paraffin  ;  when  the  paraffin  has  thickened 
a  little  by  cooling,  so  that  the  objects  when  put  into  it  will 

*  The  student  must  get  acquainted  with  the  paraffin  oven  from  an  inspection 
of  that  oven  which  happens  to  be  in  use  in  the  laboratory.  With  much  varia- 
tion in  size,  shape,  and  elaborateness  of  make,  all  the  different  ovens  in  use 
are  essentially  simply  water-baths  with  an  automatic  thermostat  for  maintaining 
a  constant  temperature. 


129 

not  sink  to  the  bottom  and  thus  have  too  thin  a  layer  of 
paraffin  below  them,  put  them  in,  with  more  melted  paraffin, 
and  with  a  warmed  dissecting  needle  arrange  them  in  posi- 
tion, i.e.,  not  too  near  each  other,  and  oriented  with  regard 
to  the  sides  of  the  paraffin  block  (that  is  to  be).  Cool  the 
paraffin  quickly  by  floating  the  tray  on  cold  water  (use  ice 
water  in  summer),  and,  as  soon  as  a  sufficiently  firm  film  has 
formed  over  the  top  of  the  paraffin,  by  plunging  the  tray 
into  the  water.  In  a  minute  or  two  the  block  will  be  hard 
enough  to  permit  of  the  unfolding  and  removal  of  the  en- 
veloping paper.  Leave  the  paraffin  block  in  the  cold  water 
for  ten  or  fifteen  minutes  at  least,  to  harden  thoroughly. 
For  very  small  specimens  the  imbedding  can  be  done  in  a 
watch  glass. 

The  specimens  are  now  imbedded,  and  may  be  preserved 
thus  indefinitely.  On  a  large  piece  of  paper  write  a  full 
label,  i.e.,  name  of  insect  and  character  of  specimen,  locality 
and  date  of  capture,  fixing  agent  employed,  and  other  de- 
tails of  preparation  that  may  be  valuable  to  know,  and  wrap 
up  the  paraffin  block  in  this  label.  Such  labelled  and 
wrapped  up  blocks  can  be  conveniently  kept  in  small 
wooden  or  pasteboard  boxes,  labelled  briefly  outside  with 
name  of  the  enclosed  specimens. 

Instead  of  paraffin,  collodion  or  celloidin  is  sometimes 
used  for  infiltrating  and  imbedding.  It  is  used  especially, 
however,  for  very  large  objects,  i.e.,  objects  more  than  one- 
half  inch  in  diameter.  For  small  objects  paraffin  is  better 
because  the  sections  can  be  cut  thinner.  For  most  insect 
work  paraffin  is  far  the  better  medium.  (For  details  of  the 
collodion  method  see  Lee's  Vade-Mecum,  p.  1 20  et  seg.,  and 
Gage,  p.  157  et  seq.) 

Section-cutting. — The  work  of  cutting  sections  with  the 
microtome  can  best  be  learned  by  the  student  by  seeing  such 
work  done.     The  differences  in  construction  of  microtomes 


I30 

with  the  varying  details  of  the  object-carriers,  knife-carriers, 
etc.,  make  it  impossible  to  attempt  here 'to  instruct  the  stu- 
dent in  the  details  of  microtome  manipulation. 

For  cutting  insect  specimens,  especially  whole  bodies  with 
their  chitinous  outer  wall,  extreme  solidity  and  rigidity  of 
the  microtome  in  all  its  parts  is  absolutely  necessary  for  ac- 
curate cutting.  The  heavy,  solidly  made,  sliding  micro- 
tomes of  the  general  character  of  the  Thoma-Jung  models 
are,  in  our  opinion,  the  microtomes  best  adapted  for  general 
insect  work.  The  cutting  is  not  done  so  rapidly  as  by  the 
wheel  microtomes,  but  the  sureness  is  an  over-balancing  item. 
Short  ribbons,  as  long  as  the  knife  is  broad,  can  be  cut  with 
the  sliding  microtomes  and  transferred  directly  to  the  slide. 

The  specimen  is  cut  as  a  small  block  out  of  the  larger 
parafifin  block  containing  it,  and  mounted  on  the  object-car- 
rier of  the  microtome.  The  block  to  be  cut  should  be  rect- 
angular in  outline,  and  be  set  with  that  margin  which  will 
first  strike  the  knife  parallel  with  the  knife.  All  screw  ad- 
justments, such  as  those  holding  the  knife  and  the  object, 
should  be  tightly  made,  and  the  block  containing  the  object 
should  be  immovably  fastened  to  the  object  carrier.  The 
sections  should  be,  for  general  work,  from  5  microns  to  10 
microns  thick.  Except  in  the  case  of  eggs  or  delicate  tissue, 
it  is  rarely  necessary  to  cut  thinner  than  5  microns. 

The  student  will  undoubtedly  meet  with  more  or  less 
trouble  in  section-cutting.  If  it  is  too  warm  in  the  labora- 
tory the  sections  may  stick  to  the  knife  ;  if  too  cold,  they 
may  roll  or  break.  Rolling  of  sections  is  the  commonest 
trouble  in  cutting.  It  is  often  apparently  impossible  to  get 
that  proper  temperature  or  condition  which  will  prevent 
rolling.  There  are  various  expedients  for  straightening  or 
hindering  the  rolling  of  sections  that  tend  to  roll.  For 
details  and  suggestions  regarding  section-cutting,  see  Lee's 
Vade-Mecum^  p.  108  et  seq. 


131 

After  the  sections  are  cut,  they  may,  if  in  ribbons,  be  kept 
on  sheets  of  paper  for  some  time  before  fastening  to  the 
slides,  but  it  is  always  advisable  for  fear  of  accident  whereby 
the  sections  may  become  lost  or  disarranged  (disarrange- 
ment of  serial  sections  is  almost  as  fatal  as  loss)  to  fasten 
them  immediately  on  to  the  glass  mounting  slides. 

TREATMENT    OF    SECTIONS. 

The  sequence  of  treatment. — The  sections  have  first 
to  be  arranged  and  faste?ied  on  the  slide,  and  have  Xht  paraffin 
removed  irom.  them  ;  then  they  have  to  be  stained,  and  finally 
cleared  and  mounted.  This  is  the  sequence  of  treatment  for 
sections  which  have  been  cut  from  a  specimen  not  stained 
in  toto.  If  the  specimen  has  been  stained  before  cutting,  the 
sequence  is,  (i)  arranging  and  fastening  on  slide,  (2)  removal 
of  paraffin,  (3)  clearing  and  mounting.  (See  also  Recapitula- 
tion, p.  138.) 

In  the  work  of  removing  paraffin,  staining,  and  clearing 
it  is  necessary  that  the  sections  fastened  on  the  slide  be 
thoroughly  bathed  by  various  fluids.  The  best  way  of  ac- 
complishing this  is  to  have  the  fluids  in  small  glass  jars. 
These  jars  should  be  of  a  diameter  slightly  greater  than  the 
width  of  the  slides  used  and  of  a  height  slightly  greater 
than  the  length  of  the  slide.  They  should  have  closely  fit- 
ting covers  to  prevent  evaporation,  and  should  be  heavy 
and  firm  enough  not  to  be  too  easily  knocked  over.  The 
so-called  Naples  jars,  or  the  Harvard  staining  jars,  or  the 
Stender  dishes  of  various  dealers  are  of  the  proper  kind. 
Ten  or  twelve  of  these  jars  containing  the  various  necessary 
fluids,  i.e.,  xylol,  absolute  alcohol,  alcohol  of  various 
strengths,  staining  mixture,  clearing  mixture,  etc.,  properly 
labelled,  should  be  arranged  on  the  table  in  an  order  corre- 
sponding to  the  successive  treatment  required  by  the  sec- 
tions. 


132 

Arranging  and  fastening  sections  on  the  slide.— 

If  serial  sections  are  being  cut  and  the  series  is  long  and  the 
sections  of  considerable  size,  larger  slides  than  the  ordinary 
3  in.  by  i  in.  slides  can  be  used  to  advantage.  For  most 
work,  however,  the  smaller  slides  do  very  well.  The  sec- 
tions are  to  be  arranged  in  regular  order  in  successive  lines 
either  parallel  with  the  short  or  long  axis  of  the  slide  as 
preferred,  leaving  uncovered  only  enough  room  at  one  end 
of  the  slide  for  a  suitable  label.  The  rows  of  sections  should 
be  near  together,  and  the  sections  near  together  in  each 
row,  i.e.,  the  paraffin  block  should,  before  cutting,  be 
trimmed  as  small  as  is  safe.  This  economizes  slides  and 
covers,  and  makes  the  series  far  more  compact  and  therefore 
more  readily  examined. 

Before  arranging  the  sections  on  the  slide,  the  slide 
should  be  very  thinly  covered  (by  rubbing  with  the  finger 
tip)  with  Mayer's  albumen  fixative  (Lee's  Vade-Meciim,.,  p. 
143),  which  can  be  bought  of  dealers  in  microscopical  sup- 
plies. Then  allow  a  few  drops  of  distilled  water  from  a 
pipette  to  flow  over  the  slide  so  that  the  sections  mdiy  float. 
This  will  straighten  out  any  folded  or  crumpled  sections. 
The  water  must  be  allowed  to  evaporate  slowly,  by  putting 
the  slide  on  top  of  the  paraffin  oven  or  otherwise  heating  it 
slightly,  being  careful  not  to  melt  the  parafifin.  After  the 
sections  are  entirely  dry,  the  slide  should  be  placed  in  the 
paraffin  oven,  and  allowed  to  remain  until  the  parafifin  is 
melted.  Or  the  slide  may  be  gently  and  carefully  warmed 
over  a  gas  or  alcohol  flame.  The  slide  should  not  be  heated 
to  a  temperature  higher  than  required  to  melt  the  parafifin. 
After  the  paraffin  is  melted  the  slide  should  be  allowed  to 
cool  until  the  parafifin  hardens  again. 

Removing  the  paraffin. — The  slide  should  now  be  put 
into  a  small  jar  of  xylol,  which  will  quickly  dissolve  the 
parafifin.     Leave  it  in  the  xylol  for  about  ten  minutes,  even 


133 

though  the  paraffin  has  apparently  been  dissolved  at  the  end 
of  three  or  four  minutes.  (The  slide  can  be  left  in  xylol,  if 
the  work  must  be  interrupted,  for  several  hours  or  even  a 
day  without  injury.)  Turpentine  or  toluol  can  be  used  in- 
stead of  xylol.  From  the  xylol  remove  the  slide  to  a  jar  of 
absolute  alcohol  (or  96^  alcohol  may  be  used),  which  will  re- 
move the  xylol.  The  slide  should  remain  in  the  alcohol  at 
least  five  minutes.  It  may  remain  longer  without  harm.  It 
should  then  be  transferred  to  a  jar  of  90^  alcohol  for  a  few 
minutes  and  then  to  a  jar  of  70^  alcohol  for  a  few  minutes. 
The  sections  are  now  ready  for  staining. 

Staining. —  The  number  of  different  "stains"  described 
in  a  manual  of  technic  such  as  Lee's  Vade-Mecum  is  so  large, 
and  the  recommendations  regarding  their  use  often  so  con- 
fusing in  the  uniformity  of  commendation,  that  the  begin- 
ning student  of  histology  is  thoroughly  at  a  loss  when  it 
comes  to  making  selection  from  such  an  embarras  de  richesses. 
For  general  work  in  insect  histology  there  is  little  demand 
for  that  large  and  growing  series  of  so-called  strictly 
chromatin  stains,  so  essential  in  cytological  work.  A  few 
nuclear  stains,  in  the  wider  sense  of  the  phrase,  a  few 
plasma  stains,  a  stain  which  will  certainly  distinguish  chitin, 
and  a  stain  or  two  especially  for  staining  in  toto,  are  all  that 
the  beginner  needs  for  most  of  his  work. 

Having  selected  a  stain,  the  student  should  bring  the  slide 
from  the  70^  alcohol  (see  above)  into  the  jar  of  staining 
fluid.  Here  the  slide  must  remain  until  the  sections  are 
thoroughly  stained  (for  time  required,  see  in  account  of 
each  stain).  Some  workers  pour  a  little  of  the  staining  fluid 
on  to  the  slide,  but  the  use  of  small  jars  full  of  staining 
fluid  is  much  to  be  preferred.  .After  the  sections  are 
stained,  they  must  be  washed  in  70^  alcohol  or  water, 
depending  upon  the  character  of  the  staining  solution  (see 
directions   in    case    of    each    stain).     They    must    then    be 


134 

dehydrated  by  bathing  with  alcohol  of  successive  strengths 
up  to  96^. 

The  following  stains  we  use  commonly  and  find  excellent 
for  most  work  : — 


FOR    STAINING    SECTIONS. 

Mayer's  acidulated  carmine  (Lee's  Vade-Mecum,  p.  174). — 
Carminic  acid,  4  grams,  distilled  water,  15  c.c,  hydrochloric 
acid,  30  drops.  Boil  till  the  carmine  is  dissolved,  and  after 
cooling  add  95  c.c,  of  alcohol  of  85^  strength  (or  for  stain- 
ing ///  toto  use  alcohol  of  95^  strength),  and  filter  the  fluid. 
After  filtering,  the  now  acid  solution  should  be  made  neutral 
by  slowly  adding  drops  of  ammonia  until  neutralization  is 
effected.  This  gives  a  beautiful,  deeply-red-colored,  and 
quickly  acting  stain.  Leave  the  slide  in  the  stain  from  five 
to  fifteen  or  twenty  minutes.  Remove  to  70^  alcohol  for 
washing  and  then  to  96^  alcohol.  It  will  be  noted  that,  in 
addition  to  the  sections,  the  thin  coating  of  albumen  fixative 
on  the  slide  has  been  slightly  stained.  This  can  be  removed 
by  passing  the  slide  quickly  through  96^  alcohol  containing 
a  very  little  (i  to  1000)  hydrochloric  acid.  This  bath  of 
acidulated  alcohol  also  "  differentiates  "  the  stain,  i.e.,  takes 
out  some  of  the  stain  from  the  cytoplasm  of  the  cells,  leav- 
ing the  cytoplasm  much  more  faintly  stained  than  the  nuclei. 
From  the  acidulated  alcohol  the  slide  should  be  removed  to 
pure  96^  alcohol.  (For  further  manipulation  see  Clearing 
and  Mounting, /^j-/^^,) 

Grenadiers  alcoholic  l)orax-car?nine  (Lee,  p,  172). — Make  a 
concentrated  solution  of  carmine  in  borax  solution  (2  to  3 
per  cent,  carmine  to  4  per  cent,  borax)  by  boiling  for  half  an 
hour  or  more  ;  dilute  it  with  about  an  equal  volume  of  70^ 
alcohol,  allow  it  to  stand  24  hours  and  filter.  Add  to  this 
solution  an  equal  amount  of  70^  alcohol ;  allow  the  mixture 


135 

to  stand  for  a  week  and  again  filter.  Especially  useful  for 
staining  in  bulk. 

DelafichVs  hctmatoxylin  (Lee,  p.  184). — This  is  one  of  the 
long  used  standard  stains  and  can  be  bought,  ready  pre- 
pared, of  any  dealer  in  microscopical  supplies.  The  formula 
for  its  making  is  as  follows  :  "  To  400  c.c.  of  saturated  solu- 
tion of  ammonia  alum  (ammonia  alum  dissolves  in  about  11 
parts  of  water)  add  4  grams  of  haematoxylin  crystals  dis- 
solved in  25  c.c.  of  strong  alcohol.  Leave  it  exposed  to  the 
light  and  air  in  an  unstoppered  bottle  for  three  or  four  days. 
Filter  and  add  100  c.c.  of  glycerin  and  100  c.c.  of  methylic 
alcohol  (CH^O).  Allow  the  solution  to  stand  until  the  color 
is  sufficiently  dark,  then  filter  and  keep  in  a  tightly  stop- 
pered bottle.  ...  It  should  be  allowed  to  'ripen  '  for  at 
least  two  months  before  using  it."  (Lee.)  For  staining, 
some  of  this  stock  solution  should  be  considerably  diluted 
with  distilled  water.  We  add  a  few  drops  of  acetic  acid  (fol- 
lowing Butschli's  suggestion)  and  get  a  much  sharper  stain. 

The  color  is  blue,  but  the  acetic  acid  produces  a  strong 
reddish  tinge.  As  this  is  an  aqueous  stain,  the  slide  should 
be  carried  from  the  70^  alcohol  (see  p.  133)  to  a  jar  of  dis- 
tilled water  before  putting  it  into  the  jar  of  staining  fluid. 
The  stain  acts  quickly,  depending  on  the  amount  of  dilu- 
tion, and  should  be  washed  out  with  water.  After  washing 
with  water,  the  slide  should  be  carried  through  50^,  70^,  and 
into  96^^  alcohol.  It  does  not  need  differentiation  (if  acetic 
acid  has  been  added)  and  the  albumen  coating  does  not  take 
up  the  stain. 

Mayer  s  /icemalufu  (Lee,  p.  182). — One  gram  of  haematein 
dissolved  with  heat  in  50  c.c.  of  905^  alcohol,  and  added  to  a 
solution  of  50  gr.  of  alum  in  a  litre  of  distilled  water.  Allow 
the  liquid  to  cool  and  settle,  and  filter  if  necessary.  A 
quickly  acting  stain.  After  staining,  the  sections  should  be 
washed  in  distilled  water. 


136 

Picric  acid. — If  desired,  and  it  will  often  be  advisable,  to 
follow  the  nuclear  stain  (any  one  of  the  preceding)  with  a 
secondary  stain,  picric  acid  can  be  employed  to  best  advan- 
tage. It  is  of  special  value  in  insect  histology  because  it 
clearly  distinguishes  chitin.  A  little  picric  acid  should  be 
added  to  a  small  jar  of  96^  alcohol  and  the  slide  passed 
through  it  before  going  into  the  pure  96^  ajcohol.  This 
bath  of  picric  alcohol  must  come  after  the  bath  of  acidulated 
alcohol  used  in  differentiating  after  Mayer's  acidulated  car- 
mine. 

Heidenhain  s  iron  hcematoxylin  (Lee's  Vade-Mecum,  p.  189). 
This  is  a  more  complicated  method  of  haematoxylin  staining, 
which,  however,  gives  excellent  and  beautiful  results  and  is 
very  helpful  in  those  cases  where  cellular  structure  is  being 
studied.  The  staining  is  done  as  follows  :  Put  sections  for 
from  one  to  two  hours  in  a  2^  to  4^  aqueous  solution  of  fer- 
ric alum  (NHJ,Fe^(SOJ^.  This  mordants  them.  Then 
wash  the  sections  -  in  water  for  from  five  to  ten  minutes. 
Then  stain  for  from  one-half  to  two  hours  in  a  y^fo  aqueous 
solution  of  haematoxylin  (made  by  taking  3  c.c.  of  a  i6fo 
alcoholic  solution  of  haematoxylin,  chloral  hydrate  2  grams, 
and  distilled  water  97  c.c).  Then  wash  the  sections  in 
water,  and  differentiate  by  dipping  the  slide  for  a  few  sec- 
onds in  the  mordant  (the  ferric  alum  solution)  and  then 
rinsing  in  tap  water,  repeating  this  operation  until  the  cor- 
rect differentiation  has  been  attained  as  ascertained  by  ex- 
amination of  the  wet  slide  under  the  microscope.  The 
chromatin  should  be  deep  blue  or  blue  black,  the  cytoplasm 
gray  or  light  blue.  After  differentiating,  the  slide  should  be 
washed  in  running  water  for  fifteen  or  twenty  minutes  to 
remove  completely  the  ferric  alum.  Considerable  practice  is 
necessary  to  obtain  the  best  results  with  this  stain.  It 
should  not  be  used  with  thick  sections,  i.e.,  thicker  than  10 
microns,  for  it  is  an  opaque  stain. 


137 


FOR    STAINING    IN    TOTO. 

If  it  is  desired  to  stain  the  insect  specimens  before  cutting 
the  sections,  a  custom  which  used  to  be  very  commonly  fol- 
lowed, but  is  being  discarded  by  many  present-day  workers, 
a  very  penetrating  stain  must  be  used.  Perhaps  the  most 
widely  used  stain  of  this  character  is  Grenacher's  alcoholic 
borax-carmine  (see  p.  134)  This  stain,  all  ready  for  use,  can 
be  bought  of  any  dealer  in  microscopical  supplies.  The 
specimens,  pieces  of  tissue  or  organs,  or  small  insects  with 
weakly  chitinized  integument,  are  taken  from  the  70^  alco- 
hol in  which  they  have  been  kept  for  a  day  after  fixing  (see 
pp.  125,  126)  and  are  put  into  this  stain  and  left  there  for 
one  or  two  days  or  even  longer,  and  then  put  into  70^  alco- 
hol which  has  been  acidulated  with  hydrochloric  acid  (i 
HCl  to  1000  alcohol)  for  differentiation.  Leave  the  speci- 
mens in  the  acidulated  alcohol  until  no  more  coloring  mat- 
ter is  being  extracted.  Then  wash  in  neutral  70^  alcohol 
and  harden  in  85^,  95^,  and  absolute  alcohol,  clear,  imbed, 
cut,  and  after  removing  the  paraffin  from  sections  in  xylol 
(see  p.  132)  mount  in  balsam  (see  below). 

Mayer's  acidulated  carmine  (see  p.  134)  can  also  be  used 
for  staining  in  bulk  as  well  as  for  staining  sections. 

Clearing  and  mounting. — The  sections  after  staining 
and  washing  and  removal  to  95^^  alcohol  have  yet  to  be 
cleared  and  mounted.  Either  cedar-wood  oil  or  xylol  or 
other  similar  oils  may  be  used.  We  use  xylol  commonly. 
The  slide  should  go  from  the  g^'^l  alcohol  into  a  jar  of  abso- 
lute alcohol  for  ten  or  fifteen  minutes  and  then  into  a  jar  of 
xylol  for  as  long  a  time.  For  mounting  use  thin  balsam  and 
no  more  than  is  necessary.  The  xylol  is  very  volatile  and 
the  mounting  must  be  done  rapidly  to  prevent  a  drying  of 
some  of  the  sections.     This  is  an  accident  to  be  carefully 


138 

avoided  throughout  the  whole  course  of  manipulation.     If 
the  sections  dry  they  are  most  likely  ruined. 

After  mounting,  put  the  slides  into  the  paraffin  oven  for 
several  hours  to  harden  the  balsam.  The  label  should  bear 
not  only  the  name  of  specimen  but,  advisably,  the  name  of 
stain  used  and  also  the  name  of  fixing  agent.  The  date  of 
mounting  should  be  added,  so  that  the  sections  may  serve  as 
tests  of  the  value  of  the  method  of  fixing  and  staining. 
Some  stains  do  not  hold  well  when  used  after  certain  fixing 
agents. 

RECAPITULATION. 

As  a  convenient  guide  for  the  beginning  student  the 
course  of  procedure  described  in  the  preceding  pages  is  here 
recapitulated  in  its  proper  sequence. 

FOR    MATERIAL    TO    BE    STAINED    IN    SECTIONS    ON    SLIDE. 

1.  Kill  and  fix  fresh  material  with  fixing  agent  (p.  124). 

2.  Wash  out  fixing  agent  with  70^  alcohol  (pp.  125,  126). 

3.  Remove  to  S^fo  alcohol  for  keeping,  or  for  beginning 
hardening  (pp.  125,  126). 

4.  Harden  in  95^  alcohol  and  absolute  alcohol  (p.  127). 

5.  Clear    in    xylol,   cedar-wood    oil    or    other   clearer    (p- 
127). 

6.  Infiltrate  with  paraffin  m  paraffin  oven  (p.  127). 

7.  Imbed  (p.  128). 

8.  Cut  sections  (p.  129). 

9.  Fasten   sections  on   slides  with   Mayer's  albumen  and 
water  (p.  132). 

10.  Remove    paraffin    from    sections   with    xylol    or   other 
agent  (p.  132). 

11.  Remove  xylol  with  absolute  alcohol  (p.  133). 

12.  Carry  through  90^  alcohol  and  70^  alcohol  (p.  133). 


139 

13-  Stain  with  Mayer's  acidulated  carmine,  Mayer's  haem- 
alum,  or  other  stain  (p.  133). 

14.  Wash  out  stain  with   70^  alcohol,  or  water  if  aqueous 
stain  is  used  (p.  133). 

15.  Remove  to  c}^fo  alcohol  (p.  134). 

16.  Differentiate  with  acidulated  95^^  alcohol  (p.  134). 

17.  Remove  to  neutral  gs^<'  alcohol  (p.  134). 

18.  Remove  to  absolute  alcohol  (p.  137). 

19.  Clear   sections    with    xylol,    cedar-wood    oil,   or   other 
clearer  (p.  137). 

20.  Mount  in  balsam, 

21.  Label. 

22.  Harden  balsam  mounts  in  paraffin  oven. 

FOR    MATERIAL    STAINED    IN    TOTO. 

Vary  the  preceding  course  of  procedure  as  follows  : 
Between  2  and  3  stain  in  toto  with  alcoholic  borax  carmine, 

or  other  stain  (p.  137) 

Omit  12  to  18  inclusive.     (It  is  possible  to  mount  directly 

after  removing  paraffin  with  xylol,  but  the  mount  is  likely 

to  be  unclean  unless  fresh  xylol  is  used  for  removal  of  the 

paraffin.) 


INDEX   AND    GLOSSARY 


Abdomen  (ab-do  men),  8,  27. 

Accessory  glands,  42. 

Accessory  veins,  110. 

Ad,  the  ending,  2 

Adipose  tissue  (ad'i-pose),  35,  56. 

Albumen  fixative,  132. 

Alcohol,  acidulated,  134,  137. 

Alimentary  canal,  36,  56. 

Anal  angle,  95. 

Anal  furrow,  94 

Anal  prolegs,  ^^ 

Anal  veins,  90. 

Angles  of  wings,  95. 

Anosia    plexippus     (A-no'si-a   plex- 

ip'pus),  84. 
Antecoxal  piece,  24,  71. 
Antennae  (an-ten'nae),  13. 
Antennal  nerves,  50. 
Antennal  sclerites,  17. 
Antennary  fossa,  13. 
Ant-lions,  wings  of,  115. 
Anus  (anus),  30. 
Aorta  (a-or'ta),  47. 
Apex  of  the  wing,  95. 
Apis  m_ellifica  (Apis  mel-lif'i-ca),  77. 
Arculus  (ar'cu-lus),  92. 
Areas  of  the  wing,  93. 
Asilid  (Asi-lid),  wing  of  an,  98. 
Aspects  of  appendages,  5. 
Aspects  of  the  body,  4. 
Attachments  of  the  alimentary  canal, 

37- 
Auditory  organs,  28. 


Basiproboscis,  84. 

Bleaching  wings,  99. 

Blood-vessels,  47. 

Boiling  water,  125. 

Bombyliid  (Bombvl'i-id),  wing  of  a, 

Braconid  (Braco-nid),  wing  of,  108. 
Branched  suspensory  muscle,  38. 
Branched  veins,  S8. 


Bullae,  94. 

Bursa  copulatrix,  45. 


Cardinal  directions,  the  six,  2. 

Cardo  (car'do),  15. 

Carmine,  134. 

Caudad  (cau'dad),  2. 

Caudal  (caudal),  2. 

Celloidin,  129. 

Cells   of  the  wings,   designation  of 

the,  92. 
Cephalad  (ceph'al-ad),  2. 
Cephalic  (ce-phal'ic),  2. 
Cerci  (cer'ci),  28. 
Cervical  sclerites,  12,  20. 
Chauliodes  (Chau-Ii'o-des),  wings  of, 

Chitin  (chi'tin),  8. 

Chloral  hydrate,  32. 

Chromo-nitric  acid,  126. 

Cicada  (Ci-ca'da),  80. 

Clearing,  127. 

Clypeal  (clyp'e-al)  suture,  64. 

Clypeo-frontal  suture,  17. 

Clypeus  (clyp'e-us),  11. 

Colleterial  (col-le-te'ri-al)  gland,  44, 

46. 
Collodion,  129. 
Compound  eyes,  9. 
Confluent,  69. 

Construction  of  the  terms  used,  2. 
Corydalis  cornuta  (Co-ryd'a-lis  cor- 

nu'ta),  31  ;   wings  of,  106. 
Cossid  (Cos'sid),  wings  of  a,  lOi 
Costa  (cos'ta),  89. 
Costal  margin,  95. 
Coxa  (coxa),  26. 
Coxal  cavities,  68. 
Cross-veins,  88,  91. 
Crura  cerebri  (cru'ra  cer'e-bri),  51. 
Crus,  51. 

Cubitus  (cu'bi-tus),  90. 
Culex,  wing  of,  99. 


141 


142 


Delafield's  hnematoxylin,  135. 

Dichotomous  branching  of  veins,  112. 

Digitus  (dig'i-tus),  67 

Diptera,  wing-veins  of,  97. 

Distad  (dis'tad),  4. 

Distal  (dis'tal),  4. 

Distiproboscis,  84. 

Dolichopodid         (Dol-i-chop'o-did), 

wing  of  a,  98. 
Dorsad  (dor'sad),  2. 
Dorsal  (dorsal),  2. 

Ectad  (ec'tad),  4. 

Ectal  (ec'tal),  4. 

Egg-calyz,  43. 

Egg-guide,  29. 

Egg-tubes,  41. 

Ejaculatory  duct,  40. 

Elytra  (ely-tra),  72. 

Embryology,  material  for   study  of, 

124. 
Empidid  (Em'pi-did),  wing  of  an,  98. 
Entad  (en'tad),  4. 
Ental  (en'tal),  4. 
Entire,  69. 

Epicranial  suture,  17. 
Epicranium  (ep-i-cra'ni-um),  10,  64. 
Epimeron  (ep  i-me'ron),  24. 
Epipharynx  (ep-i-phar'ynx),  18,  85. 
Epipleura  (ep-i-pleu  ra),  68,  72. 
Episternum  (ep-i-ster'num),  22,  24 

Fastening  sections  on  slide,  132. 

Fat,  35,  56. 

Femur  (fe  mur),  26. 

P'irst,  second,  third,  etc.,  5. 

Fixative,  132. 

Fixing,  124. 

Flabellum  (fla-bel'lum),  79. 

Fleniming's  chromo-aceto-osmic 

acid,  126. 
Frenate  moths,  wings  of,  loi. 
Frenulum  (fren'u-lum),  99. 
Frenulum  hook,  102. 
Front,  II. 

Frontal  ganglion,  51. 
Frontal  ridge,  64. 
Furcula  (fur'cu-la),  28. 
Furrows  of  the  wing,  94. 

Galea  (ga'le-a').  15. 

Ganglia  (gan'gli-a),  34. 

Gastric  caeca  (gas'tric  cae'ca),  36. 


Genae  (ge'nae),  11. 
Generalized,  87. 
Glossa  (glos'sa),  19,  67. 
Grenacher's  borax  carmin,  134. 
Great-dorsal-recti-muscles,  53. 
Cireat-ventral-recti-muscles,  53. 
Gula  (gula),  65. 
Gular  (gu  lar)  sutures,  66. 

Ilaemalum,  135. 

Ilaematoxylin,   135,  136. 

Hardening,  127. 

Head,  7. 

Head,  parts  of  the,  9. 

Heart,  47. 

Jlepialus    (He-pi'a-lus),     wings    of, 

lOI. 

Hermann's  platino-aceto-osmic  acid, 

126. 
Histoblasts,  61. 

Histology,  methods  of  insect,  121. 
Holorusia  rubiginosa,  54. 
Honey-bee,  wing  of,  108. 
Plumeral  angle,  95. 
Humeral  cross-vein,  91. 
Hymenoptera,  wings  of,  102. 
Hypopharynx  (hypo-pharynx),    14, 

20,  77. 
Hypothetical  type  of  wing.  96. 

Ichneumon-fly,  wing  of,   108. 
fmaginal  buds,  61. 
Imbedding,  127. 
Infiltrating,  127. 
Inner  margin,  95. 
Intermediate,  6. 
Interrupted,  72. 
Intestinal  caecum,  57. 
Intestine,  37,  56. 
Intima  (in'ti-ma),  46. 
Iron  haematoxylin,  136. 

Jugular  sclerites  (ju'gu-lar  scle'rites), 

Jugum  (ju'gum),  loi. 

Killing,  124. 

Krauss,  Dr.  William  C.,  51. 

Labella  (la-bella),  84, 
Labial  palpi  (la'bi-al  palpi),  14. 
Labium  (la'bi-um),  14. 
Labrum  (la  brum),  11. 


143 


Lacinia  (la-cin'i-a),  15. 
Laterad  (later-ad),  2. 
Lateral  (lat'er-al),  2. 
Lateral  filaments,  ^^. 
Legs,  26. 

Lepidoptera,  wings  of,  99. 
Ligament  of  the  viscera,  39,  42. 
Ligula  (lig'u-la),  14,  20. 
Limitations  to  accuracy,  6. 
Locusts,  7. 

Longitudinal  veins,  88. 
Lora,  79. 
Lyonet,  51. 

Macroxyela  (Mac-rox"y-e'la),  103. 

Malpighian  vessels  (Mal-pe'ghi-an 
or  Mal-pig'hi-an),  36,  56. 

Mandibles  (man'di-bles),  13. 

Mandibular  scrobe,  66. 

Margins  of  wings,  95. 

Masticatory  organs  of  the  proven - 
triculus,  39. 

Maxillae  (max  illae),  13,  15. 

Maxillary  palpus  (max'il-la-ry  pal- 
pus), 16. 

Maxillary  segment,  17. 

Maxillary  tendons,  84. 

Mayer's  acidulated  carmine,  134. 

Mayer's  albumen  fixative,  132. 

Mayer's  haemalum,  135. 

Media  (Me'di-a),  90. 

Medial  cross-vein,  92. 

Median  furrow,  94. 

Medio-cubital  cross-vein,  92. 

Mediproboscis,  84. 

Melanoplus  femur-rubrum  (Me-lan'o- 
plus  fe'mur-ru'brum),  7. 

Mentum  (men'tum),  14. 

Mercuro-nitric  mixture,  126. 

Mesad  (mes'ad),  3. 

Mesal  (mes'al),  3. 

Meson  (mes'on),  3. 

Mesonotum  (mes-o-no'tum),  21,  22. 

Mesosternellum,  24. 

Mesosternum  (mes-o-ster'num),  23. 

Mesothorax  (mes-o-tho'rax),  22. 

Metanotum  (met-a-no'tum),  21,  22. 

Metasternellum,  24. 

Metasternum  (met-a-ster'num),  24. 

Metathorax  (met-a-tho'rax),  22. 

Micropyle,  45. 

Monarch  Butterfly,  wings  of  the, 
101. 


Mounting  sections,  137. 
Mouth  parts  of  a  locust,  13. 

of  a  butterfly,  84. 

of  a  cockroach,  18. 

of  a  cicada,  80. 

of  the  honey-bee,  77. 

of  a  hornet,  75. 

of  the  horse-fly,  82. 

of  the  house-fly,  83. 
Musca  domestica,  83. 
Muscid,  wing  of  a,  98. 
Muscles,  51. 

Nervous  system,  50. 
Neuroptera,  wings  of,  108. 
Nodal  furrow,  95. 
Numbering  of  wing-veins,  90. 

Oblique  lines,  3. 

Obsolete,  9. 

Occiput  (oc'ci-put),  II, 

Ocelli  (o-cel'li),  9. 

Ocellus  (o-cellus),  9. 

(Esophagus  (oe-soph'a-gus),  36. 

Ommatidium  (om-ma-tid'i-um),  9. 

Open,  69. 

Optic  nerves,  51. 

Outer  lobe,  15. 

Outer  margin,  95. 

Ovaries,  41,  43,  46,  58. 

Oviduct  (o'vi-duct),  29,  41. 

Ovipositor  (o-vi-pos'i-tor),  28. 

Palpifer  (pal'pi-fer),   15. 
Palpiger  (pal'pi-ger),   14. 
Pamphilius  (Pam-phil'i-us),   103. 
Parafifin,  infiltrating  with,  127. 
Paraffin ,  removing,  132. 
Paraglossae  (par-a-glos'sas),  19,  67. 
Patagia  (pa-ta'gi-a),  99. 
Penis,  42. 

Pericardial  diaphragm,  48. 
Peritremes  (per'i-tremes),  24. 
Pharynx  (pharynx),  36. 
Picric  acid,  136. 
Picro-aceto-sublimate,  125. 
Picro-sulphuric  acid,  126. 
Pleurite  (pleu  rite),  28. 
Pleurum  (pleu'rum),  28. 
Plica  (plica),  72. 
Podical  ([)od'i-cal),  plates,  28. 
Postgenae  (post-genae),  12. 
Postmedia  (post-me'di-a),  90. 


144 


Postscutellum  (post-scu-tel'lum),  21. 
Priescutum  (I'raf-scu'tum),  21. 
Premedia  (pre-me'di-a),  90. 
Preservation  of  specimens,  32. 
Prolegs,  33. 

Pronotum  (pro-no'tum),  21. 
Propygidium  (pro-py-gid'i-um),  73. 
Prosternellum,  22. 
Presternum  (pro-ster'num),  21. 
Prothorax  (pro-tho'rax),  21. 
Proventriculus      (pro-ven-tric'u-lus), 

Proximad  (prox  im-ad),  4. 
Proximal  (prox'i-mal),  4. 
Pseudotracheae      (pseu-do-tra'cheae), 

Pterostichus  californicus  (Pte-ros'ti- 

chus  cal-i-for'ni-cus),  63. 
PulviUi  (pul-vil'li^,  26. 
Pygidium  (py-gid  i-um),  73. 

Radial  cross-vein,  91. 

Radial  sector,  9b. 

Radio-medial  cross-vein,  91. 

Radius  (ra'di-us),  89. 

Recti  muscles.  53- 

Rectum,  37,  57. 

Removing  paraffin,  132. 

Reproductive  organs,  40. 

Respiratory  system,  46. 

Rhyphus  (Rhy'phus),  wing  of,  87. 

Rolling  of  sections,  130. 

Salivary  glands,  57- 

Scenopinid  (Sce-nop  i-nid),  98. 

Sclerites  (scle  rites),  8. 

Scutellum  (scu-tel  lum),  21,  23. 

Scutum  (scutum),  21,  23. 

Section  cutting,   129. 

Seminal  vesicles,  42,  46. 

Sequence   of    treatment   of   material, 

124. 
Setigerous  (se-tig'er-ous)   punctures, 

.65- 
Sialis  (Si  a  lis),  wings  of,   115- 
Simple  eyes,  10. 
Simple  suspensory  muscle,  38. 
Simple  veins,  88. 
Siricid  (Si-ric'id),  wing  of,  108. 
Small-dorsal-recti-muscles,  53. 
Specialization  by  addition,   109. 

by  reduction,  109. 
Specialized,  87. 


Spermatheca  (sper-ma-the'ca),  44. 
Spermatozoa  (sper  ma-to-zo'a),  43. 
Sphecid,  wing  of,  108. 
Spiracles   (spir'a-cles  or  spi'ra-clesj. 

24.  57- 
Spurious  vein,  99. 
Sternite  (ster'nite),  28. 
Sternellum,  21. 
Sternum  (sternum),  21,  28. 
Stigma,  103. 
Stipes  (stipes),  15. 
Stomach,  36. 
Stylets,  82. 

Subcosta  (sub-cos'ta),  89. 
Subcostal  fold,  94. 
Subgalea  (sub-ga'le-a),  66. 
Submentum  (sub-men'tum),  14. 
Suboesophageal     ganglion      (sub-oe- 

sophag'e-al),  51. 
Superior  lobe,   15. 
Supracesophageal  ganglia  (su-pra-oe- 

soph-ag'e-al),  50. 
Suspensoria  (sus-pen-so'ri-a),  of  the 

viscera,  37. 
Suspensory  muscles,  38. 
Suspensory  nerves  of  the  alimentary 

canal,  39,  49. 
Sutures  (sut'urs),  9. 
Sympathetic  nervous  system,  59. 
Syrphid,  wing  of  a,  98. 

Tabanid,  wing  of,  98. 

Tabanus  (Ta-ba'nus),  82 

Tsenidia  (tae-nid'i-a),  47. 

Tarsus  (tarsus),  26. 

Technical     nomenclature,     need     of 

a,  I. 
Tegmina  (teg'mi-na)  27. 
Tenthredinids  (Ten'thre-din'ids, 

wings  of),  108. 
Tentorium  (ten-to'ri-um),  12,  17. 
Tergite  (ter'gite),  28. 
Tergum  (ter'gum),  28. 
Testes,  40,  41,  46. 
Testicular  follicles,  40. 
Thorax  (thorax),  8;   parts  of,  20. 
Tibia  (tib'i-a),  26. 
Tipulid,  54. 

Tracheae  (tra'che-ae),  46. 
Tracheal  gills  (tra'che  al),  23- 
Tracheation  of  wings,  117. 
Trochanter  (tro-chan'ter),  26. 
Trochantin  (tro-chan'tin),  26. 


i4i 


Tympanum  (tym  pa-num),  28. 
Typical  branching  of  the  wing-veins, 
95- 

I'pper  lobe,  15. 

N'agina,  41. 

\'agus  ner\-e  (vagus),  51. 

Vasa  defeientia  (va'sa  def-e-ren'ti-a), 

40. 
Vas  deferens  (vas  deferens),  40. 
X'enation  of  the  wings,  86. 
\entrad  (ven'trad),  2. 
Ventral  (ventral),  2. 
Ventral  diaphragm,  4g. 
\  entriculus  (ven-tric  u-lus),  36. 
Vertex  (vertex),  11. 
Vespa  maculata,  75. 

Ward,  the  suffix,  2. 
Wing-covers,  27. 
Wings,  27. 
Wings  of  the  heart,  48. 

of  ant-lions,  1 15. 

of  an  Asilid,  98. 


Wings  of  a  Bombyliid,  y8. 

of  a  Braconid,  108. 

of  Chauliodes,  115. 

of  Corydalis,  115. 

of  a  Cossid,  loi. 

of  Culex,  99. 

of  Dolichopodids,  98. 

of  an  Kmpidid,  98. 

of  frenate  moths,   loi. 

of  Hepialus,  loi. 

of  a  Honey-bee,  108. 

of  Hymenoptera,   102. 

of  an  Ichneumon-fly,  108. 

of  Lepidoptera,  99. 

of  the  Monarch  butterfly,   loi, 

of  a  Muscid,  98. 

of  Neuroptera,  108. 

of  Rhyphus,  87. 

of  Scenopinid,  98. 

of  Sialis,  115. 

of  a  Siricid,  108. 

of  a  Sphecid,  108. 

of  a  Syrphid,  98. 

of  a  Tabanid,  98. 

of  Tenthredinids,  108. 
Wing-veins,  86. 


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